Naomasa Tsukauchi/Synopsis

History
Naomasa Tsukauchi is the eldest son of the Tsukauchi family. After his little sister, Makoto Tsukauchi, manifested her Polygraph Quirk for the first time, she kept asking Naomasa sometimes uncomfortable questions, to know if he was telling the truth or not. This bothered Naomasa and asked her sister to stop, although their mother asked him to just humor her.

Years later, he joined the Police Force and became a detective.

Vigilantes Beginnings Arc
Led by his partner Eizo Tanuma, Naomasa is part of the investigation into the “Villain Out-Break Incidents" in Naruhata over the past few weeks. All these incidents are related to the use of the drug called Trigger, that boost an individual's Quirk, but turned into a villain instantly.

The police managed to arrest several of these "Instant Villains" although, many of them were previously defeated by a local vigilante group known as Naruhata Vigilantes. Although they help keep the peace, Naomasa tells his partner Sanza that there is something called the law, and carrying out personal acts of vigilantism is a crime. The former Instant Villains are interrogated, and each of them has been confirmed to use the drug moments before their attacks, and that they acquired it from a stranger who gave it to them without demanding anything in return.

Eizo, believes that since Trigger has been distributed in specific places they could track down the dealers, however is confused as to why the dealers would hand Trigger out for free, considering that it is a very valuable product. Naomasa ponders about the objective the dealers want to achieve. Eizo notes that "objective" is the keyword and surmises that the dealers may want to make a massive profit or an upheaval of public order, although he may be overthinking this.

One of the Instant Villains that was defeated by the Naruhata Vigilantes is Teruo Unagisawa. After interrogating him, they decide to release him, but he is followed by Naomasa. Kuin Hachisuka, one of Trigger's main distributors, uses his Queen Bee Quirk to transform innocent people into Instant Villains and cause an outbreak. Naomasa immediately calls for backup, and numerous heroes appear and subdue the Instant Villains. The situation is controlled, but Naomasa finds that Teruo has disappeared, having been kidnapped by Kuin for unknown reasons.

Because innocent people have been involved in this incident, Eizo sent Naomasa to request All Might's help in dealing with the Trigger outbreak, specifically telling him to talk to his secretary-manager, Toshinori Yagi, if All Might wasn't available. Naomasa goes to the Might Tower and meets Mr. Yagi, not knowing that he is actually All Might in his base form.

While they are having a conversation in a café, Toshinori constantly makes excuses and run to perform quick deeds as All Might. When Toshinori accidentally returns with the uniform still visible (revealing his dual identity as All Might), Naomasa calls him out on not filing reports on all of his heroic activities, as customary of a Professional Hero. Taking pity on the number 1 Hero, Naomasa offers to file the reports himself, letting All Might act without any worries apart from telling Naomasa what he is doing.

The next day, Naomasa receives several cases of All Might's unplanned Heroics and wonders if it was Eizo's plan to push All Might's ordeal onto him from the start.

During the following days, the incidents with the Instant Villains continue to happen, as well as their defeats at the hands of the Naruhata Vigilantes.

Vs. Queen Bee Arc
After a day of work Naomasa returns to her apartment where his sister Makoto also lives. She is working on her thesis on vigilantism, and asks her brother, since he is a detective at the police station, about any villains or hero information he has learned of, but he replies that he cannot leak any confidential information. He warns her not to approach suspicious individuals out of curiosity.

She interprets his warning as "don't screw up", much to Naomasa frustration, and he replies firmly that what he is saying is that she does not put herself in danger for the sake of obtaining information for her thesis. As a result of his research, Makoto ends up meeting Koichi and Kazuho, ​​discovering that they are the Naruhata Vigilantes, but decides to hide that information from her brother. She also becomes Pop's manager.

One night, Shota Aizawa, known as the Hero Eraser Head, defeats Teruo Unagisawa, who this time presents a very strange physique. When the police arrive and take Teruo, Naomasa Tsukauchi approaches Eraser Head and introduces himself as one of the investigators of the incidents related to the intant Villians and wants to ask some questions about the fight.

Eraser tells Tsukauchi that he doesn't think Teruo is an instant villain, and did not see any injector on him. However, he tells him, he did see a bee on the villain. Tsukauchi mentions that many civilians mentioned getting stung by a bee during the mass outbreak of instant villains.

Osaka Incident Arc
Days later, Naomasa has a conversation with Eraser Head and the Midnight. He talks about the new villains that had begun appearing throughout the city. He tells them that Teruo Unagisawa had been arrested twice for being an "Instant Villain", however, he had undergone a drastic change between his first and second arrests in that his physical form had completely changed and it seemed to be at least semi-permanent.

In addition, the police had found several other villains with similar alterations that had concentrations of Trigger present in them which was several grades higher than the lethal dose of the drug. This had led the Police Force to suspect that someone had purposefully altered their bodies to withstand higher doses of Trigger.

Naomasa tells Shota and Midnight that he believes there is an organization behind the distribution of Trigger that is also administering to others and altering them to be able to withstand greater amounts of the drug. For the time being, the police calls this organization the Villain Factory.

Shota says that the organization must have some greater goal in mind because by themselves their "Instant Villains" and "Next-Level Villains" could not do much and were more like disposable pawns. Naomasa agrees and says that is why he had come, to ask for Shota's help in the matter.

Naomasa's investigations on Trigger's traffic take him to Osaka, specifically to the SS Mall in Super Minami, a shopping/dining district. Apparently, the police suspect that the Villain Factory uses Kanidoge chain, specialized in crab food, to import and distribute the drug. For this operation, they have an infiltrated agent, Monika Kaniyashiki, as a worker in the Kanidoge chain; and Fat Gum in case of needing a Hero for the operation.

When carrying out her research work, Monika goes to the loading docks and analyzes a batch of Kanidoge products. When opening a box, she sees that there are only crab and icepacks in two different sizes, nothing out of the ordinary, which is lampshade by one of the loading docks workers. However, Monika points a gun at him asking who he is. The suspect says he is only a part-time worker, but Monika tells her that she knows each and every one of part-timers who work there. She also realizes that the drug is hidden in the icepacks of the product, and she gets a tablet that contains important information about smuggling operations.

Having been discovered, the suspect uses his Quirk, which gives him enormous speed, to snatch Monika's pistol and tablet. She quickly asks for reinforcements, so Naomasa, Fat Gum and the rest of the police forces come to the place to catch the suspect.

Monika warns Naomasa to be careful as the villain has an acceleration Quirk that gives him extreme speed. When seen surrounded, the villain activates a code that causes several of the mechs employed by the workers are out of control and go on a rampage. Thanks to Fat Gum and Monika, the workers are rescued and the mechs are neutralized, however, they explode destroying all the evidence. The villain (known as Number 6) takes advantage of the confusion to flee with the remaining evidence using his Quirk.

While Fat Gum and Monika leave to deal with a Mech that is still active, Naomasa and the remaining Police Force chase the suspect. Naomasa manages to hit him in the leg with a shot, deducting that his acceleration Quirk needs a cool down time after using it.

Confronted by the police, the villain uses his Quirk again. In a blink of an eye, he disarms a whole group of cops and shoots in their bulletproof vests with their own weapons. Although this does not kill them, it does leave the police very badly wounded. The Villain being able to finally escape with the clues without any problem.

Naomasa ends up with several fractures and the arm in a sling, but still continues with the investigation of the Villain Factory. Since Kazuho was involved in the incident (albeit against her will), Naomasa wants to question her and Koichi, who is also there, but they both leave before he has a chance. However, he manages to obtain their business card, and is surprised to find that his sister’s name on the card as event coordinator.

Sky Egg Arc
Naomasa returns to Tokyo, where she meets All Might again in the Might Tower cafeteria. The hero is surprised to see Naomasa seriously injured, and when he knows the causes, he tells Naomasa that that if he had known, he would have help him. Naomasa thanks you for your concern, but tells All Might that a public figure like him can’t be taking jobs for personal reasons neither prioritizing saving certain people because they could be taken hostage or use as a diversion by villains. Toshinori can not deny that he is right.

Upon finishing his meeting with All Might, Naomasa returns to his apartment. Upon discovering that Makoto is Pop☆Step's manager, he ends up having an argument with his sister. Naomasa wants to interrogate her because the incident in addition to her past as a Vigilante, but Makoto protects Kazuho and will not let him treat her like a criminal, assuring him that she has abandoned his life as a Vigilante and now has a legal occupation as an idol.

Later, Naomasa and Shota Aizawa goes to the Hotta brothers' shop to meet with Kirihito Kamachi, to talk about his kidnapping by the Villain Factory, but he, the only thing that complains is that today's society discriminates against those who are physically different, like him.

Along with Eizo Tanuma, he analyzes a security cam tape about the failed attempt to arrest the speedster villain in Osaka. Eizo suggests that he may be one of those people who are so fast that for them the rest of the world seems like frozen in time. This gives Naomasa the idea of meeting with Shota, who tells him about O'Clock, a speedster-type hero of the previous generation who suddenly disappeared without a trace. O'Clock had a very similar Quirk to the Villain’s, and everything seems to indicate that there is some connection between them.

The investigation on the distribution of the trigger and the speedster villain continues. Days later, Naomasa informs Eraser Head about the existence of a new variant of Trigger, that only needs to be ingested to work. This new drug is connected to the instant villains who attended to Mixers, so the police suspect the drug is mixed into the drinks, and the victims are getting roofied. He asks Shota for help, but since he does not like to have to attend parties of any kind, he suggests that Midnight be the one to participate in considering it more appropriate for that kind of mission.

Shota's decision proves to be right, as Midnight manages to find the one responsible for drugging the drinks with Trigger, capturing her and giving her to the police. Midnight is congratulated by Naomasa for the work done.

From the subsequent interrogation and investigation, he learns that the new orally administered Trigger, it's less effective that the regular version but does not turn people into full-blown villains, so it makes it easier for the Villain Factory to distribute it and search potential candidates to kidnap and transform into Next-Level Villains. He also learns that Number 6 is the main responsible for its distribution. The investigation led the police to the place where the deals were happening, but they’d already cleared out. Also, the new trigger came from China, out of Japanese jurisdiction. Naomasa reports to Eraser Head all this new info.

Thanks to the information that was given to him by anonymous sources and to an arduous investigation, detective Naomasa manages to locate the place where the Villain Factory carry out its illegal experiments for the creation of the Next-Level Villains with the consumers of Trigger that its agents kidnap. The Villain Factory’s laboratories are located in an isolated area of the Onomura Pharma Corp., a medium-sized pharmaceutical company.

Once determined the place, Naomasa organizes the police forces to carry out a raid. For the operation, they will have the help of the heroes Eraser Head and Fat Gum, in case they have to face serious threats. With everything ready, on the same day that the Captain Celebrity's farewell show is being held at the Tokyo Sky Egg, police forces surround Onomura’s main building and assault it.

The Police Force and the Heroes move quickly through the building until they reach the secret laboratories, arresting all suspicious workers and confiscating all possible evidence in the process. Once in the labs, they meet Number 6, surrounded by creatures known as Bombers. Before the police or the heroes can stop him, Number 6 activates a device that causes several of the Bombers to explode, destroying the labs. The villain manages to escape with five of the Bombers, with the objective of attacking the Tokyo Sky Egg and killing Captain Celebrity.

Fortunately, Naomasa and his allies manage to survive the explosion thanks to Fat Gum, and along with Shota, flies quickly by helicopter to the Tokyo Sky Egg. There Shota uses his Erasure Quirk to help the heroes who are fighting the Bombers, and managing to defeat the creatures. However, Shota fears that the enemy has another trick up his sleeve, and asks Naomasa to call All Might for help.The detective is somewhat reluctant to summon the number one hero for a mere precaution, but Aizawa tells him that they are dealing with an unprecedented crisis, with thousand lives at stake, so it's not the time to get carried away by the regulation and normatives.

Naomasa agrees to Aizawa's request and calls All Might. Naomasa tells him that the Tokyo Sky Egg is in trouble, but before he can clarify him the situation, Number 6 succeeded in getting the building to collapse by causing one of the Bombers to self-destruct. Naomasa watches impotently as the building collapses, with thousands of people inside, including his sister Makoto Tsukauchi. Then he desperately asks All Might to save his sister. Thanks to this, All Might arrives in no time to landing the Tokyo Sky Egg dome safely and saving everyone.

Journalists and reporters arrive to report the Bombers' attack on the Tokyo Sky Egg, and ask All Might about his opinion. After his statement, he says goodbye and runs away, being pursued by the media. After elude them, All Might, now as Toshinori Yagi, returns to the place and meets secretly with Naomasa. He tells him that he’s going to stick around for a while in case there’s another attack.

Naomasa apologizes for getting bent out of shape, but Yagi tells him that it’s fine and that it was his impassioned plea that got him there in time. Yagi explains to Naomasa that his Quirk has a strong psychological component to his strength. When he hears a plea for help, he feels it like a direct order to All Might. He tells him that when he accepted his power in order to save everyone and give them hope.

Naomasa feels confused about he "accepted" his power, and All Might realizes that he has unwittingly revealed an important fact regarding One For All and its secrets. Before their conversation continues, they are interrupted by Shota Aizawa, Fat Gum and Monika, and Naomasa introduces them to Yagi, who thinks that one of these days he will have to explain Naomasa everything about the secret behind All Might.

Number 6 does not give up, and attacks again sending a swarm of Mini-bombers, but transformed back into its muscular form, All Might destroys all creatures, being cheered by those present. Then he disappears again to meet Naomasa as Toshinori Yagi.

Days later, Naomasa asks his sister Makoto to convey a message to Koichi: Due his actions, he acknowledges that The Crawler deserves to be recognized for what he did, as his intervention helped to save thousands of lives, yet his acts of vigilantism remain illegal. Therefore, the police have put in a request to the heroes and other witnesses to keep quiet about him. But he clarifies that his success during the Sky Egg Bombing only bought him a free pass from the police this time, and it would be nice to not go around lauding him as some kind of hero. Finally, Naomasa says that he is grateful for what he did.

A few days later, his sister Makoto left for the USA to study abroad at a college in New York, in addition to continuing to be Captain Celebrity's manager.

At some point between the Sky Egg Bombing and All Might becoming a teacher at U.A., All Might reveals the truth behind One For All to Naomasa, gaining him as a valuable ally in the fight against the villain All For One.

Final Performance Arc
Years pass in Naruhata, and since the Sky Egg Bombing, no serious incident has occurred in the city. Koichi has continued to work as the vigilante The Crawler, and his sister Makoto has plans to return to Japan after two successful years in the United States of America. Yet one day, without any explanation, Kazuho Haneyama, known as Pop☆Step and partner of The Crawler, rampages Naruhata, bombarding the streets with a swarm of exploding bees, causing destruction and commotion everywhere before leaving, but not before promising that she will return for an even better "Show" than that.

Because of this criminal act, she is registered and considered a villain. From New York, Makoto phones his brother upon knowing the news and she maintains a heated argument with him. She complains about Kazuho being treated as a villain, but her brother quickly clips back that Pop is a wanted suspect for a large-scale Quirk based attack, and the fact that she’s labeled as a villain means she won’t be treated as a minor.

Makoto tries to find a hole in those statements when Naomasa tells her to quit arguing just for the sake of it. Makoto breaks down in tears. Naomasa is aware of his sister's frustration and her desire to help Kazuho. He knows she feels responsible for the girl but warns her to stay where she is and do not try to return to Japan at that time to do something inappropriate.

Naomasa tries to comfort his sister, telling her that her time to help Kazuho will come because the media is gonna spin this in whatever way that they want to. Makoto then asks him about Koichi's whereabouts, because if there is anyone who can help Kazuho at that time, it's Koichi. Unfortunately, Koichi has been missing since the attack.

In the days following Pop's rampage, the police and the heroes organize patrols through the streets of Naruhata, to protect its inhabitants while fixing the damage caused by the bombing, and as well as being ready in case Pop decides to return to attack, just as she had promised. A week later, Pop decides to attack Naruhata again to the sound of her music. The heroes stationed there try to stop her, but Pop uses her Bomb Bees to make them fail in their attempts, causing even more destruction.

On a rooftop not far from there, detective Naomasa observes Bee☆Pop easily outmaneuver the heroes on patrol, taking advantage of the lack of teamwork due to their hasty formation and having cut off communications with her bees. Next to him is the number two Hero Endeavor,, ready to end Pop's criminal career.

Detective Naomasa discusses with Endeavor and reminds him that the mission is to capture Pop☆Step. The problem is that Endeavor considers the villain too dangerous. He states that Pop Step has a Quirk powerful enough to blow up the town with ease. Therefore, the best option is to annihilate her by wide-scale assault, leaving Naomasa in absolute shock. Before the detective can answer him, Endeavor receives a message from his Flaming Sidekickers that everything is ready for him to take action.

Endeavor uses his Super Move Hellfire Storm, releasing an intense hellfire tornado towards Pop, leaving Naomasa impressed. The detective realizes that although it may give the impression of being a crude attack, Endeavor is actually controlling the tornado precisely to minimize damage to the city. Pop is about to be engulfed by the giant whirlwind of flames, but Endeavor is forced to cancel his attack when he is informed of the presence of another person in the area.

Angry, Endeavor shouts out to Naomasa that he though they ordered everyone to get out. Naomasa realizes that the intruder is none other than Koichi, sliding down the streets going after Pop, and tells to Endeavor he is the Naruhata Vigilante, The Crawler. The enraged Endeavor claims that a vigilante is nothing more than another villain to dispose of.

But for the moment Endeavor will have to wait, because he needs to cool down his body for deveral minutes due to the overheat caused by his Quirk. Naomasa Tsukauchi warns the others to pull back as Bee☆Pop is headed their way with her explosions. Endeavor refuses to simply back down and instead commands the detective to deploy the patrol squad.Naomasa agrees to his request, considering that the rest of the heroes will be able to apprehend Pop and the Crawler, although Endeavor tells him that the only thing he needs is 5 minutes before going back into action.

From their position, both Naomasa and Endeavor watch as both Pop and The Crawler manage to dodge the rest of the heroes, until they face each other. Pop plays a new theme song, and Naomasa points out that the explosions have changed patterns and that it kind of looks like a mid-air battle or a game of tag is taking place now. Naomasa continues to observe the fight from afar, and sees that Pop apparently manages to defeat The Crawler and then gather all the bomb bees around her. Endeavor deduces that Bee☆Pop is planning to blow herself up, ending her life.

However, something happens to Pop and she is knocked down, falling into an alley and being rescued by The Crawler. A few minutes later, the vigilante appears with Pop in his arms and seemingly running away from a swarm of bomb bees exploding around him. Once his cool down is over, Endeavor is ready to stop both of them and uses his super move Hell Minefield.

Naomasa sees Koichi being caught in the flames of the attack, but without anyone expecting it, The Crawler uses Slide and Glide to blast off into the sky with Pop☆Step, leaving everyone dumbfounded. Naomasa can't help but be surprised to see Koichi flying.

In the aftermath of Pop☆Step's capture, Naomasa goes to the maximum security hospital in which she is admitted. After being bioscanned and checked by an officer, he meets Midnight and Kazuho's mother inside. Naomasa points out the high security of the hospital, to which Midnight replies that Soga Kugisaki and his friends were insistent on this. She explains that since she was admitted, the hospital received inquiries from unidentified individuals, setting the alarms off. Midnight tells Naomasa while she would prefer to have Kazuho transferred to a more secure and isolated facility, she is in no condition to be moved.

Later, Naomasa individually interrogates and questions Moyuru Tochi, Rapt Tokage, and Soga Kugisaki. While Moyuru and Rapt tell conflicting alibis to why they were near the spot where Kazuho and Koichi fell, Soga keeps his mouth and glares at the detective. Naomasa attempts to reason with him that they are not treating him and his friends as criminals and that Kazuho is not a typical villain, but they need information to work with. Soga replies that Naomasa should just talk to Kazuho if he wants answers, and asks if she is out of surgery, to which Naomasa confirms, and that Midnight asked him to give any updates.

Naomasa informs Soga that while the Queen Bee had been successfully extracted, Kazuho has not yet regained consciousness and will probably suffer long-term consequences. He also explains that while Midnight told him that Soga and his friends saved Kazuho, he is choosing to believe that it was actually Koichi Haimawari, The Crawler, who saved her. He wants to know where he is, but Soga says that he cannot give his location away as he must do what he can to protect Kazuho.

Running out of patience, Naomasa shouts at Soga, saying that this is not the time for vigilantism as several people have already died because of the incident. Soga instead replies that if the deaths are weighing on him, maybe he and the police should do their job properly. Naomasa remains silent for a moment, until Soga asks him to bring in detective Eizo, to which he reluctantly complies.

Eizo is brought in, and recognizes Soga from his involvement with Trigger a few years back. He notices that Soga has a different feel to him now, reminding him of a certain ally. Soga proceeds to talk about an analogy Knuckleduster told him about, amusing Eizo.

Eizo later lets him and his friends go, bewildering Naomasa, while the former tells him that it is better to pit troublesome people like them against actual villains. Looking down at the trio walking away, Naomasa tells him that he will continue watching them and The Crawler, while Eizo nonchalantly pokes fun at his uptightness.

Naruhata Lockdown Arc
Sometime after the attack on the police station, which left Eizo in critical condition, Naomasa contacted several Pro Heroes in preparation to arrest The Crawler. He is contacted by Makoto, who tries to get her brother to reveal information about the situation, but to no avail. Naomasa reflects on how he knows that the attack was part of a plot to hinder the Naruhata investigation, silently admitting to himself that Soga may be right about the police needing to do a better job. Sansa soon arrives with an arrest warrant for Koichi Haimawari, as Naomasa reaffirms that as authority figures, they must not allow themselves to rely on outlaws, as doing so would be admitting that the justice system has failed. The two then head out to put an end to the Naruhata Vigilantes once and for all.

The next day, Naomasa and his squad confront Soga and his friends, who were guarding Kazuho's hospital on their own. Naomasa declares that they will be in charge of securing the ward now and that his group will be cooperating with the investigation. While Soga agrees, he points out how the police took too long to take action. He continues by saying that the police aren't prepared to devote their resources to protect Kazuho, and criticizes that due to the nature of how the system is set up, they are not capable of catching things that fall through the cracks of the system.

Midnight tries to play the mediator between both groups, but Naomasa jumps in and mentions that they have an arrest warrant for Koichi. He claims that if left on his own, Koichi may encounter a real villain and result in causing more damage. Soga asks if he believes that Koichi is unprepared, to which Naomasa rebuts that it's because he is prepared that it is a problem. He commands Soga to call Koichi, to which he reluctantly complies. However, Soga instead gives Koichi a "Wake Up Call" telling him to escape, and runs away from the police himself. Naomasa orders half of his police force to follow him after Soga, but Midnight reminds him that they are supposed to guard the hospital. Midnight calls Naomasa a terrible negotiator, to which he agrees.

Naomasa gives a signal to Team Idaten, informing them that their negotiations have failed, so they deploy Ingenium to catch The Crawler. He then receives a report from them about Koichi being on the run and how Eraser Head and the other Heroes are closing in on his location. Midnight then receives a call from Soga who asks to speak with Naomasa. He apologizes for giving him the slip, and saying that he was intending to negotiate with him after Koichi had escaped, unaware that he sent a whole group of Heroes after him.

Soga tells Naomasa to call off the Heroes because there’s no point in extending their cat and mouse game, that all they want to do is guard the hospital, and that they’ll accept any punishment once it is all over. Naomasa still refuses to budge, but Soga mentions how Eizo Tanuma is someone who’d try to meet in the middle, and that he knows the two groups being at each other’s throats is what the enemy wants.

Soga is right, as Number 6 takes advantage of the Heroes, Vigilantes, and Police Force fighting amongst themselves to execute Operation Anonymous, using a group of drone villains known as the Anonymous to shut down the power in the city, while also causing minor disturbances throughout. Naomasa tries to figure out what’s going on, recognizing all this as a coordinated attack, and thinks about how to contact the head office, and a police officer approaches him regarding the status of the hospital wing.

Naomasa and his Police Force meet back up with Midnight and the doctors as they try to get power back up in the building, as well as detailing their priority on the situation. Rapt then appears to Naomasa, telling him Soga’s arrived and wants to talk to him alone.

They chat in the parking garage, where Soga tells him that since they can’t contact the Heroes right now, they have to be prepared with whoever is available. They both go over all the information they know of on Number 6: that Koichi told them he was going to murder Kazuho, and that he’s a speedster who loves being sneaky and using disguises. Naomasa also recalls his previous run-in with him, how they have been looking for him for a while, and that they suspect he’s the one who went after Eizo.

Soga comes up with a plan to distract his speed by sniping at him from the corridor, which Naomasa agrees, but tells him not to hit him, as he can’t let a civilian get his hands dirty, and to let his officers finish the job. Soga agrees to these terms, saying he doesn’t think he could easily hit him anyway from that distance, and that he’ll let them handle it.

Number 6 soon arrives at the hospital, using the Anonymous to force his way inside, and makes it into a hallway where he's confronted by Naomasa and several officers who attempt to place him under arrest. Number 6 recognizes Naomasa from the Osaka incident, as well as pointing out he referred to him by “Overclock”, which he figures means Eizo told him about his Quirk, and that he should of shut him up sooner, as the officers are all shocked by Number 6’s completely crisped face. He tells them that he’s only here to kill Kazuho, but if they get in the way they’ll be on his list too, until he is surprised by the shots coming through the window from Soga directly outside.

He switches the gun to automatic, causing random fire throughout the hallway, which Naomasa thinks about being a bit too much. Number 6 intends to wait until the gun is out of ammo to catch his breath, but is instead surprised by the arrival of Koichi, who utilizes his Shooty-Go-Blam to further distract Number 6. He continues to try and dodge and swat away the low-impact attacks, which allow the officers the opportunity to shoot at Number 6 at the legs, causing him to fall on his knees, as Naomasa yells to secure him.

They manage to restrain Number 6 with cuffs that include a stun function. Naomasa gets them to call Midnight, as she heads over there, however, parts of Number 6's body suddenly start to melt away as the others react in confusion, until he uses Overclock to freeze time and remerge his body to go right in front of Naomasa, taunting him that since his body is made up of Bomber cells that take commands from his brain, shooting his hands and legs won’t do anything, and he should’ve aimed for the head.

As he prepares to take down the officers for being too slow, Koichi starts blasting more Shooty-Go-Blam shots at his face, forcing Number 6 to flee. Koichi is shocked at his speed, while Naomasa quickly turns to him for a task: to leave and go get All Might for help.

Number 6 then sends a group of Anonymous to attack Naomasa, but they shut down once they arrive, as a result of Koichi facing down Number 6, allowing the police to apprehend them and Midnight to put them to sleep. Naomasa then hears explosions going on outside, as a result of Koichi and Number 6's battle.

U.S.J. Arc
Outside U.A. High School, Naomasa checks the status of Class 1-A and determines that everyone (except Izuku Midoriya) is unharmed. He then tells Class 1-A to head back to their class. Tsuyu Asui asks him the condition of Shota Aizawa, to which he replies that he is in a critical state but not life-threatening and says that although Thirteen and All Might are injured, they are not in a critical state and are being treated by Recovery Girl. Naomasa then asks Nezu whether he can investigate U.A., which the principal allows.

Naomasa then visits U.A.'s Nurse Office, friendly greeting All Might. All Might asks him about the status of the students as well as Thirteen and Shota, to which Naomasa states that the students are fine and the teachers are not in life-threatening danger. He then says that if he, Thirteen and Shota had not fought the villains, the kids would probably be in a terrible condition, but All Might says that the students also fought bravely and made those villains look like fools and concludes that they will make fine heroes which Naomasa smiles to.

U.A. Sports Festival Arc
In a meeting with U.A.'s staff, Naomasa tells them that he has investigated the villains Tomura Shigaraki and Kurogiri but could not find any information about them. He then says that they captured and arrested 72 villains at the Unforeseen Simulation Joint and says that they were all third rate thugs, however, the problem was that all of them seemingly swore allegiance to Tomura.

Naomasa insinuates that in an age filled to the brim with heroes, villains must have felt pressurized and that is why they decided to follow Tomura's "innocent" simple-minded brand of evil. Naomasa says that he is going to assist in enlarging the police force so that they can continue capturing more criminals.

Vs. Hero Killer Arc
Naomasa meets with All Might at U.A. He tells All Might that the Police Force have tried everything to get information out of Nomu, however, everything they tried did not work. Naomasa says that they instead looked into Nomu's background through DNA analysis and have discovered that Nomu was once a human with a criminal record. Naomasa explains that the DNA analysis also revealed that the Nomu has the DNA of at least four different humans mixed with his own. Naomasa concludes that Nomu is an artificial human made to measure up to multiple Quirks and that having all the DNA in his body as well as his body modified caused Nomu's brain activity to stop.

Naomasa tells All Might the real issue is that Nomu's DNA is of primary concern because it contains multiple Quirks. Naomasa says that Nomu could not have acquired multiple Quirks in any way (unless Nomu acquired the Quirks through advanced genetic familial permeation). Naomasa comes to the conclusion that someone with a Quirk that can grant Quirks is behind Nomu's acquisition of multiple Quirks, much to All Might's horror.

Forest Training Camp Arc
After the incident at Kiyashi Ward Shopping Mall. Naomasa arrives at the scene and takes Izuku to the Police Station to be questioned by him about the event that transpired. At the Police Station, Naomasa questions Izuku about Tomura and their conversation. Although the information Izuku provides is nothing new, Naomasa thanks Izuku for the information and praises Izuku for being level headed during his confrontation with Tomura. The Police investigator is glad with Izuku's actions because collateral damage was kept to a minimum and no lives were lost.

Outside the Police Station, All Might greets Izuku and Naomasa; he apologizes to Izuku for not being there. After All Might answers Izuku's question and Izuku along with his mother leave, Naomasa theorizes that Tomura will probably target other students and decides that Hero schools must exercise more caution and become more proactive in implementing counter measures against villains. Naomasa advises All Might that leaving U.A. is also an option, but All Might decides against it. Naomasa concludes their conversation by saying that they will capture All For One this time, to which All Might agrees.

Hideout Raid Arc
One day after Katsuki Bakugo is captured by the League of Villains' Vanguard Action Squad, Naomasa phones All Might to inform him that there has been an unexpected development; they have probably located the League of Villains hideout. Naomasa plans a rescue operation after this top-secret intelligence has been verified and asks Toshinori to join the operation. The hero thanks Naomasa for his hard work and plans to get payback once he has found the villains.

A day later at night, Naomasa along with the Police Force and a large number of Pro Heroes wait near the League of Villains' hideout. Naomasa reminds the Pro Heroes of the importance of the rescue operation, that the Hero Society may fall if they do not succeed. Naomasa states that they know the hideout Katsuki is in and tells the Pro Hero team that while investing their efforts in rescuing Katsuki, they will capture the other hideouts to block off the League of Villains’ escape route and then apprehend the villains themselves.

The time for the pro heroes and the Police Force to initiate the rescue operation has come; Naomasa tells everyone that the rescue operation is a battle of speed and to not let any villains retaliate. Naomasa reveals that U.A.'s public apology broadcast was to deceive the villains into thinking that the heroes were having a hard time and could not afford to attack today; thus the pro heroes and the Police Force have the element of surprise on their side for their counter-attack since the League of Villains are not expecting them to attack now. The pro heroes and the Police Force head out and stand in front of the League of Villains' hideout, preparing to storm the place.

The pro heroes storm the League of Villains hideout and apprehend Tomura and his fellow villains while another group of pro heroes infiltrate and take control of the League of Villains' warehouse. However, All For One intervenes and summons multiple Nomu while Tomura and his fellow villains escape. Naomasa and the pro heroes deal with the Nomus while All Might goes to chase after All For One. Eventually, they manage to apprehend all Nomus.

All Might manages to defeat All For One at the cost of losing the One For All forever. Naomasa and Gran Torino visit All Might in hospital. All Might who is bandaged and recovering states that he can no longer use One For All and that although he can no longer be the Symbol of Peace, he still has things to do. Naomasa is in disbelief that Tomura Shigaraki is Nana Shimura's grandson. On that topic, Gran Torino comments that Nana Shimura and her husband had a child. However, after her husband died due to heroics, Nana sent her son to a foster family so that he can stay away from the world of heroics. Nana then informed Gran Torino and All Might to not get involved with her son.

All Might wishes to find Tomura, however, Gran Torino tells All Might that he is in no position to help Tomura since he has would not be able to see Tomura as a villain. Gran Torino and Naomasa decide that they will handle the search for Tomura. Gran Torino suggests to All Might that he must remain at U.A and carry out what he must still do; helping his successor, Izuku Midoriya.

Shie Hassaikai Arc
Thanks to the investigations of the police, Naomasa Tsukauchi and Gran Torino have managed to track down and find Kurogiri with the help of eyewitness reports and have subdued him. Gran Torino tells Kurogiri that if they arrest him, the League of Villains will fall apart. As Naomasa warns Gran Torino about Kurogiri's Quirk, Kurogiri asks Gran Torino if he knows of the rumors about a "ruffian" appearing on the mountain where they are at and the reason he is here is to speak to the "ruffian".

Gran Torino would prefer Kurogiri to tell him all about it behind bars. Suddenly, a huge noise reverberates in the area which catches Gran Torino's attention. An enormous beast that towers over trees appears with a boombox around his neck, which surprises Gran Torino. Kurogiri states that the ruffian is one of All For One's faithful servants: Gigantomachia.

He and Naomasa are seriously injured and the task force suffer severe casualties at the hands of Gigantomachia, but they manage to take Kurogiri into police custody, at the cost of allowing Gigantomachia to escape, after having completely destroyed a large portion of the mountain. Later, Gran Torino phones All Might to inform him about all of this.

Endeavor Agency Arc
By the end of December, Naomasa has been assisted All Might with tracking down information about the past users of One For All, to provide to Izuku. By Christmas time, Nezu talks to All Might and detective Naomasa through a video call. They talk about the fact that since all the students moved into Heights Alliance four months ago, they have been being watched to discover the League’s spy, but in all that time no one has shown signs of being the spy, so it seems that the traitor is not one of them.

Paranormal Liberation War Arc
Since Kurogiri was captured and imprisoned in Tartarus, Naomasa and Gran Torino have been interogating him to obtain information about the League of Villains. However, Kurogiri only talks about useless stuff, becoming unresponsive when bringing up the League of Villains, Like his power's been cut.

This has led them to decide to carry out a series of analyzes to study the nature of Kurogiri, discovering two important aspects about him: the first one he is some kind of special Nomu, and the second is that for his creation, All For One used the corpse of a former U.A. student as base, Oboro Shirakumo. With the latter data, Naomasa and Gran Torino decide to call Shota Aizawa and Hizashi Yamada to help them, since they were Oboro's best friends when they were students, and they inform them of the latest discoveries and ask them to come to Tartarus.

Once the altered Shota and Hizashi arrive to Tartarus, Naomasa and Gran Torino explain in more detail the situation and the plan. They have discovered that intelligent Nomus retain part of their personality when they were human, so they hope that, since they were friends of Oboro, Naomasa tells Shota and Hizashi that he wants both to reawaken Oboro's lingering "attachment" toward his old life so they can get information for the investigation. Hizashi questions if it shouldn't be the Oboro's family who does that to which Naomasa says they will contact them if they fails, but Shota doesn't want the Oboro family to know the horrible truth and sets out to follow Naomasa's plan.

Shota and Hizashi enter the interrogation room to awaken Oboro's memories in Kurogiri. Not without great insistence, they manage to get Oboro to overcome Kurogiri's control for a brief moment and says "hospital" before the fog hides his face again and Kurogiri falls unconscious. Naomasa congratulates both heroes for their help. Later, at the prison front door, Shota and Hizashi say goodbye to Naomasa and Gran Torino. Shota would have liked to have been more helpful, but Naomasa corrects him that thanks to them they have made progress.

After Shota and Hizashi leave, Naomasa calls the Public Safety Commission President to tell her the last clue obtained. Then, the commission called to Hawks, who is working as a mole in the Paranormal Liberation Front, the fusion between the League of Villains and the Meta Liberation Army, to tell him this info, which turns out to be an important clue in his investigation. With this information, plus the information Hawks later obtains from Twice, who trusts him without knowing his double agent nature, they manage to determine that Shigaraki is hiding in Jaku General Hospital.

Naomasa sends an undercover agent to the hospital, while they also investigate its founder and current board chairman Kyudai Garaki for several months. In the end, all their work pays off as they discover that Dr. Garaki is an ally of All For One, and in the Jaku General Hospital there is an area that does not appear in the blueprints that only Dr. Daraki can enter.

With this information plus that provided by Hawks about the plans of the Paranormal Liberation Front, the police and heroes decide to organize a raid against the Jaku General Hospital and the Gunga Mountain Villa in order to take down the criminal organization and arrest their members. Days before the raid, Naomasa organizes a meeting with various heroes where he explains to them about who Kyudai Garaki is.

Endeavor asks the detective how they realized that Jaku General Hospital is the main objective and what "he" is doing, but Naomasa doesn’t tell him anything saying that it’s highly classified information and he doesn't know who he means by “he”. He just replies that everyone is working hard for the peace of the country. The number one Hero does not insist asking, being sure that it is Hawks who is behind it all.

By the end of March everything is ready. The heroes involved in the operation are divided into several groups: one will be in charge of storming the village, another led by Endeavor will be in charge of arresting Garaki in the hospital, and one made up mainly of students will be in charge of evacuating the inhabitants of a city near the hospital. Naomasa and a large police force are part of the Endeavor group.

Kyudai is aghast at the unexpected appearance of the heroes and tries to flee, but he is captured by Eraser Head, who uses his Erasure Quirk on him. Kyudai grows older, which shows that he has some kind of Longevity Quirk, and he isn't Quirkless as it appears in the Quirk Registry. Naomasa supposes it's the secret behind All For One's longevity. He also notes that the Quirks they have seen, such as Super Regeneration, seem "rare", and perhaps those Quirks were either replicated or created artificially to help All For One.

When they decide to take Kyudai, the hospital is invaded by numerous Nomu, who attack the heroes and seriously injure the doctor, who dissolves because of the wounds showing that he is not really the real one but a Double.

Despite the Heroes attempts to shut down Tomura, he manages to awaken and the entire hospital is destroyed by the enhanced power of Tomura's Decay. Despite the numerous casualties, Naomasa is able to escape and survive the encounter.

Tartarus Escapees Arc
In the aftermath of the Paranormal Liberation War, the destruction of major cities, and many of the villains' escape, Naomasa, alongside the rest of the Police Force, work alongside the Heroes for clean-up as best as they can do, despite the shortage in resources. After about a month, All Might has an encounter with Stain, who gave him a data disk that he had acquired when he escaped from Tartarus.

All Might gives the information to Naomasa to analyze, who's slightly annoyed at needing to have gotten help from a killer. He reveals that since Tartarus’ systems are cut off from the outside world, they would’ve had no way of getting this data normally, and that it contains the cause of the system shutdown, which was “Tomura” and All For One’s constant blasts of Radio Waves inside and out.

Sansa suggests that this is because All For One was synchronized with the vestige within Tomura, however All Might reveals that the communication isn’t a two-way channel. Just like with his vestige within One For All, while the vestige has access to all his current thoughts, All Might himself has no connection to the vestige itself, at least until he was able to make contact with Izuku back at the Hospital. Because of this, All Might believes that even All For One wouldn’t be able to have such direct control over the vestige from so far away.

Naomasa then says that the two All For One's were able to communicate through the Radio Waves Quirks, and that the recorded waveforms on the data disk resemble a conversation that says: “Make him complete in 38 days.” The revelation shocks Sansa, as Central Hospital’s research stated it was 2 months till he was completed, but All Might says it’s possible he rigged the results as a bluff, and that if they are to take their conversation as the truth, Tomura will be complete in 3 days.

Star and Stripe Arc
Due to this sudden revelation, All Might calls for immediate aid from the foreign heroes. America's No. 1 Hero, Star and Stripe heads over with her pilot crew for assistance, planning to rendezvous with Japan's Top 3 Pro Heroes. On the way, Naomasa ends up warning the three heroes that something has gotten in Star and Stripe's way from their planned meet-up point: Tomura has shown himself.

The two battle, and while Star ends up losing her life and having her Quirk, New Order, stolen, it results it the Quirk acting like a virus within Tomura, forcing him to once again retreat and attempt to heal. Shortly after the battle, Star's pilots go to see All Might, Naomasa, and the Police, who tell them her sacrifice was not in vain, while All Might sadly laments about wanting to see her again. The pilots tell them their fighter jets have a record of the battle, and were able to measure all of Tomura's bio-signatures, as well as every Quirk during the fight, providing the data to them to use, alongside the ones already being studied at Central Hospital.

U.A. Traitor Arc
While studying this information, everyone is forced to respond to another devastating revelation: Yuga Aoyama and his family have been spies for All For One and were just discovered and apprehended by Izuku. In the U.A. A.V. Room, the Aoyamas are interrogated by All Might, Naomasa, and the U.A. staff, learning Yuga received his Quirk about 10 years ago, and that he doesn’t seem to be rigged to explode like Lady Nagant was. Nezu asks the students to leave the room, but a devastated Class 1-A bluntly refuse.

Naomasa asks the parents all they know about All For One, with the father saying they know nothing, only that they carried out his orders, and if they failed or lied, they would be killed, having been shown the bloody remains of someone who tried to go to the police in the past. The father continues to beg that it was only them who are at fault and Yuga had no idea. Yuga begins to break down, thinking about everyone that could’ve died because of him, yet he still had the nerve to smile with everyone like they were friends. Especially after seeing Izuku, another former Quirkless person, fighting so hard againt All For One, made him realize how pathetic he was, wallowing in his own despair, and that he’s just a villain through and through.

However, Izuku retorts, asking why he tried to save Katsuki and Fumikage during the Training Camp, as well as asking about the cheese message, realizing that it was a cry for help, and that’s why he’s crying now. He continues that he knows of another Hero who was manipulated by All For One, but her soul wasn’t crushed, only her spirit. He states that doing wrong doesn’t make you a villain for the rest of your life, as he extends his hand to Yuga, telling him that he can still be a hero.

In response to Izuku's pleas, Naomasa gets Sansa to cover up Yuga's mouth. He reminds Izuku that no matter the circumstances, he still conspired with All For One, and they still aren't sure if he's booby-trapped like Lady Nagant, so they can't allow him to talk again until he's examined at Central Hospital.

Naomasa continues to interrogate the Aoyama parents, with them revealing they didn't report to All For One about the Kamino Incident since they could only communicate with him when he contacted them, but Izuku cuts him off, reminding them that they have no way of locating All For One. This leads the rest of the students to realize that they can use Yuga as a way to deceive All For One.

Present Mic asks Class 1-A why, with them being the greatest victims after all this, they're so willing to trust him. Tenya simply responds that what happened is in the past, and with them being unable to realize how he's been feeling all this time, they carry some responsibility, so they must reach out to him as friends in order for them to become equals again.

Naomasa reminds the class that the Aoyamas already told them All For One won't believe any lies so they need to keep a level head, when Izuku is called on by Shota Aizawa, watching from a tablet held by Present Mic. He asks Izuku if he has a plan, with Izuku responding that he doesn't. Shota then addresses Naomasa, taking full responsibility for also not recognizing Yuga's pain and siding with the rest of the class, informing Yuga he has no intention of expelling him from U.A.

Shota reveals that he has an idea, and after the Aoyama Family's ears have been covered, he informs Class 1-A, the U.A. Staff, and the Police Force of his plan. After the discussion, Nezu states that it seems possible, while Naomasa has the Aoyama Family escorted back to their HQ, telling everyone not to say a word to anyone else about the plan. Before he leaves, Izuku shouts out to Yuga, with the rest of the class looking on sullenly.

At Central Hospital, the “League of Villains/Paranormal Liberation Front Counter-Force” has assembled with All Might and Hawks addressing the Police Force, American military, and former hero Ragdoll. They mention how due to Yuga's situation, they’re ready to move ahead after deeming everyone involved trustworthy. Hawks continues that Endeavor, Best Jeanist, and the other big Heroes are currently in command out in the field, so they’ll be keeping their current circle small to detail the classified information.

All Might places tiny buttons of All For One and Tomura on a whiteboard, stating that whether they’re going for Plan A or B, what they must do no matter what is to split them up. Based on the data from the fight against Star and Stripe, they realize Tomura has far surpassed All For One in power, recalling his fight in Kamino as an example of the latter’s strength. He also refers to the “mind meld” they exploited during the Assault on Tartarus, unsure of the full extent of their shared consciousness beyond communication with Radio Waves, saying that if they were to attack together, they’d have no hope of victory.

One of the pilots ask why they didn’t work together to fight Star, which All Might believes is because All For One would potentially be vulnerable to New Order, with her speaking his name. He states that they must at least separate them by a minimum of 10 kilometers if they want a chance at victory.

Naomasa adds that they know the Villains will do everything to make sure that won’t happen, with All Might bringing up the threat of Dabi’s flames and how he could single-handedly stop them in their tracks. Ragdoll takes this as meaning they first need to isolate Dabi, before All Might clarifies that they’ll need to isolate all of them: separating each of the League's major operatives, luring them out individually, and defeating them one by one.

Several men say it’s easier said than done, with All Might responding they need to have a strategy to make it happen, which Naomasa figures is Yuga. He adds that while he does sympathize with his situation, considering he still turned his back on society, from his position he still has to proceed with caution. All Might says he chooses to believe in Yuga, and he already believes in his teacher.