Koichi Haimawari/Synopsis

History
When he was a baby, he was able to float before he could even walk. As he would tend to float out of his crib, and even towards roads into traffic, his worried mother would use her Fly-Swatter Quirk on him whenever he floated, possibly conditioning him into not using it and causing him to forget that he even had the ability.

Later on in life, Koichi started impersonating All Might while interfering in fights, putting himself in danger to help people. Koichi was determined to be a hero, but the morning of the high school entrance exam, he stopped to save a drowning child. He gave the child his silver age All Might hoodie to keep warm, and then rushed off to the exam, for which he was too late.

Having lost his chance to become a hero, Koichi decides to study Hero Sociology at the college. When he moved to Naruhata, he rented out a old penthouse on top of an old building for a cheap price. At the time, Koichi thought it was a good penthouse to live in as it would easily kick start his campus life. One night, he wanted to invite some friends to his home, but due to a misunderstanding, he was seen as a perverted and dangerous student, making many of his colleagues to avoid him. As a result, Koichi's campus life debut was a failure.

To earn money for rent, start working as a clerk at a convenience store. It is also when he begins to "work" as a vigilante, doing good deeds for the public, which makes him being appreciate by the citizens, who start to refer to him as "Nice Guy".

Formation of the Vigilantes of Naruhata
One day, while on his way to his workplace, Koichi stumbles into a group of thugs and knocks into Soga Kugizaki, which spills the juice he just bought. The thug orders Koichi to apologize by getting down and groveling, to which Koichi obeys, but Soga wants to humiliate him, so he escapes, being chased by Soga and his friend Moyuru and Raputo, until they lose his track.

Later, Koichi sees another group praising a freelance idol, Pop☆Step. A police vehicle is passing by, so Koichi warns Pop☆Step. As she ends her live performance, Koichi slides to his place of work. Customers arrive, however, they are Soga and his buddies. Soga takes Koichi outside and beats him up, threatens him with spikes. After being forced to buy juice for Soga, Koichi is annoyed at being beaten up and changes into his "suit", an All Might-styled jacket and a mouth mask. Koichi decides to deliver justice on his own accord, which basically is doing public services such as returning dropped items, giving directions, recycling, etc... The citizens thank Koichi who feels overjoyed in helping people.

With his good deeds done for the day, Koichi begins walking home. He meets Kazuho again in an alley. She thanks him for warning her about the Police and followed him in order to properly thank him, but she make fun of him for being weak and wearing an All Might hoodie, which causes both to start arguing. Pop☆Step begins to leave but bumps into Soga and his friends. The thugs recognize her as the online idol, begin mocking her and even thinking to sexually assault her.

Scared, at first Koichi thinks about leaving her to her fate, but seeing her scared face decides to help her without thinking. He does not have much success at first, and all he gets is to anger Soga even more. Soga decides to finish off Koichi with his Quirk for annoying him.

Suddenly, Knuckleduster appears, crashing down onto a trash heap. He defeats the thugs and checks their tongues to see if they’re discolored, but cannot find anything. Then, Knuckleduster turns his attention to Koichi and praises him for his efforts. Suddenly, Soga takes Pop☆Step hostage, threatening to claw her face off, but Koichi charges at the thug and knocks him down, allowing Pop☆Step to escape and Knuckleduster to punch Soga into the wall, which knocks him out. Impressed by Koichi's bravery, Knuckleduster decides to take him as his disciple to make him a hero, despite not having the license. However, Koichi finds Knuckleduster to be dangerous and turns down his offer.

Next morning, Koichi returns to his apartment, only to find Knuckleduster there. Knuckleduster does not mind if Koichi calls him "master", but Koichi has no intention of becoming his disciple. He explains that he is dedicated to hunt down dealers and users of Trigger, a drug that significantly boost the user's Quirk, but in return the users become more violent. Knuckleduster states that their mission is to confront any thugs and make them stick out their tongues because Trigger causes tongues to turn into a hideous black color. Knuckleduster explains that they will beat them, make them talk about the dealer who gave them the drug and cut off the circulation of Trigger. Koichi thinks that Knuckleduster is not being serious.

However, to Koichi's misfortune, Knuckleduster is dead serious, and his method of investigation consists of hit first and ask later. Pop☆Step arrives and decides to help them by searching on the internet for "sudden villain appearances" which will allow them to pinpoint the location of the Trigger Junkies. In that moment Knuckleduster spots Mario Kugutsu, a salesman who looks suspicious to him, and tries to interrogate him by force.

Pop☆Step and Koichi try to stop the old man to no avail, but at that moment Aizawa appears, who tries to stop Knuckleduster under the suspicion of being a villain, which causes Knuckleduster and Shota to start fighting, much to Koichi and Pop☆Step's shock. Koichi apologizes to the salesman and asks him to declare his and Pop☆Step's innocence to Shota but the salesman leaves in a hurry. Pop☆Step realizes that Mario appears in the pictures of villain disturbances. She and Koichi run after him because he is suspicious.

In their pursuit, Koichi and Pop meet Soga, Moyuru and Raputo, now transformed into Impromptu Villains thanks to the Trigger that Mario had given them previously, and attacked them. Soga and Moyuru chase Koichi, but are defeated by Shota and Knuckleduster who had stopped fighting. For her part, Pop continues pursuing Mario, being pursued by Raputo in turn. The salesman inject himself with Trigger, growing into a colossal giant with four arms.

The giant grabs Pop☆Step and Raputo with his hands, swinging them about. Hardly, Knuckleduster and Koichi manage to rescue Pop, and the colossal salesman starts shrinking and returns back to normal when Shota activated his Erasure  on him, disabled Mario’s Quirk. Shota wraps his cloth around the salesman. The Police Force arrive and arrest the salesman and the three thugs.

In a back alley, Pop☆Step is relieved that Koichi is alright, but he thinks that he is not cut out to be a Hero. Knuckleduster appears and is pleased by Koichi’s bravery. Knuckleduster knows that Koichi's spontaneous words and actions are actually his true feelings; that he still aspires to be a Hero. Knuckleduster encourages Koichi to chase after his aspiration to be a Hero. Thus, Koichi's life as a Vigilante begin from a lonely back alley and he would eventually go on to reach for greater heights.

The Vigilante "The Crawler"
After having accepted Knuckleduster as his master, Koichi is trained by him, who gives him equipment and advices to better exploit his Quirk. Knuckleduster also told Koichi that he needed a new name, as "Nice Guy" would cause evildoers to make light of him, so he chooses The Crawler as his new vigilante name.

They also begin to conduct patrols together through the streets of Naruhata, confronting any villain they meet. Some are mere troublemakers, but others are Trigger users, known as Impromptu Villains. The first one is Akira Iwako, a villain with a Hardering Quirk that Knuckleduster and Koichi manage to defeat by collaborating together, then leaving him tied to be arrested by the police. Their actions call the attention of Detective Naomasa, who is in charge of the police investigation of everything related to the illegal traffic of Trigger and the Impromptu Villains.

The next threat is Teruo Unagisawa, a big fan of Pop☆Step who, in his desire to be closer to her, injects to himself a dose of Trigger transforming into an eel-like creature. Teruo chases Pop through the alleys of Naruhata, but Knuckleduster and Koichi set a trap and defeat him, then leave it to the police. All in all, they want to ask him about the Tigger he used, so they go looking for him after the police release him. However, Kuin Hachisuka, a villain who works for the mysterious organization responsible for the Trigger incidents, causes an Impromptu Villains outbreak after injecting Trigger to several innocent people with their quirk, taking advantage of the resulting chaos to take Teruo with her to an unknown place.

It turns out that Kuin works for the Villain Factory, a mysterious criminal organization responsible for distributing Trigger, and therefore, for the incidents with the Impromptu Villains. For unknown reasons, the Villain Factory searches for people with particular characteristics and Quirks, and the drug is the key element to find these individuals. This is the reason why their agents are dedicated to distribute the drug free of charge between thugs and petty criminals. Fulfilling his mission, Kuin gives Trigger to a junkie, who begins to cause problems until he is defeated by the Vigilantes of Naruhata.

One day, doing exercises with his Slide Quirk, Koichi meets Tensei Iida, better known as Turbo Hero: Ingenium. the two hit it off with Tensei offering advice on how to use his Quirk more effectively, and after seeing that Koichi has potential, he even giving him a card and a job offer at his hero office. Kouchi is more than ecstatic for it because he can fulfill his dream. However, he reveals he's a vigilante when he helps stop Bat Villain. While Tensei is more than happy for the help and doesn't report him, he ends up asking for the card back since he can't endorse what is essentially a lawbreaker, much to Kouichi's dismay.

Days later, Koichi meets Stendhal, a Vigilante like him, who saves his life while fighting against Akira Iwako. Stendhal's attacks force Iwako to flee, and Koichi thanks him for saving him and asks him his name. Stendhal presents himself before leaving in pursuit of the villain. This meeting made a great impression on Koichi, who star gushing over Stendhal. However, everything changes when he knows his true nature and personality. Unknown to Koichi, Stendhal had allied with Kuin Hachisuka and was engaged in hunting and kill former Trigger users. This is the reason why, when they meet again, Stendhal tries to kill Soga. Koichi tries to save Soga and run away with him on his back. Stendhal praises Koichi's innate act of goodness but since he side with evil have evil within themselves, and try to kill him too, until Knuckleduster arrives just in time to save Koichi Haimawari and Soga Kugizaki by defeating Stendhal in a straight fight.

Meeting Makoto and Captain Celebrity
After the run in with Stendhal, Koichi Haimawari resumes his life at college. However, he is struggling with his Heroics Sociology course. Makoto Tsukauchi, a female college student, approaches him despite having a negative reputation in the university after a misunderstanding, and decided to help him with his studies. This help is accompanied with the ulterior motive to use him as help for her thesis about Vigilantism. She asks him to do a field survey investigating the rumored "Vigilantes of Naruhata". Despite being surprised and nervous about her request, since he is one of them, Koichi agrees to help her.

After being helped with his studies, the next day Koichi accompanies Makoto, who reveals that the purpose of her investigation is to find out how well the "Vigilantes of Naruhata" are accepted by the populace. Koichi and Makoto spend the morning asking the locals about their opinions towards the Vigilantes, and later Makoto compiles all the information in her laptop. Suddenly, it is stolen from her by a thief but Koichi is able to retrieve it. Makoto thanks him for his help and gives him a hand shake while also asking him one final question. As they shake hands, Makoto activate her Polygraph Quirk, and asks Koichi if he is “the Hauler”; the name by which his Vigilante persona is known by the population. However, since Koichi sees himself as "The Crawler", he replies he is not “the Hauler", and pass her Quirk's test since he's telling the truth. Makoto apologizes for her question and returns to her house to continue working on his thesis, wonders if her intuition is getting stale.

Days later, Koichi is chasing a thief on a motorbike. The villain uses his Long Legs Quirk to kick Koichi, who is about to hit a truck but is suddenly rescued by Christopher Skyline, a.k.a. Captain Celebrity, who also apprehends the thief. The new Hero suggests Koichi to leave the dangerous jobs to the pros. Koichi starts to think badly about Captain Celebrity, considering him an arrogant, egotistic person and more interested in gaining fame and popularity than doing well his work as a hero. This opinion does not improve when he discovers that Makoto - for whom Koichi has a little crush - is part of Christopher Skyline’s cheerleading group, and due to his womanizer attitude, he invited her to a date to flirt with her. However, all attempts to seduce her abandoned Captain Celebrity when Makoto told him that she became friends with his ex-wife, and she is in contact with her. From that moment, Makoto went from one of the Captain Celebrity cheerleaders to her boss.

One day, he gets a call from his dad who tell him the terrible news that his mother is coming to Tokyo for a visit and that she’s already on train. This has Koichi try to clean up his room as quickly as possible, saying to Kazuho that his mother is very strict with him. He remembers his updates to her, including one that states he has a girlfriend. In fear for being scolded for lying, he asks Makoto to pose as his girlfriend. However, when Shoko arrives a mets Makoto for the first time, she realizes at once that everything is a farce and scold Koichi. Despite this, Makoto and Koichi’s mother quickly become friends, and Shoko decides to stay longer to go sightseeing in Tokyo with Koichi and Makoto. She also meets Kazuho and Knuckleduster, posing as mister Kuroiwa.

Koichi spends the next morning with Makoto and his mother touring Tokyo, but when they get on the bus that will take them back, Kuin Hachisuka decides to cause another havoc by injecting Trigger to a cat with quirk. The cat hops on to the bus and morph into a cat bus with his Monster Cat Quirk. The vehicle goes out of control. Everyone in the bus is panicking until Ingenium comes to the rescue as he enters the bus. The driver informs him he cannot stop the bus, which can cause an accident if it crash. Thanks to Knuckleduster manage to swerve the cat bus in a different direction. It is on an express lane, heading to a destroyed overpass and giving a five minute time-limit to the heroes. Team Idaten rescue almost all the passengers. However, Kuin gives the cat an extra dose of Trigger, causing it to move away with Makoto still on board.

Koichi, disguise as the Crawler, and Tensei collaborate together to save Makoto before the bus falls through the edge. Koichi enters the bus and rescues Makoto, as it begins to free fall from the expressway. Ingenium uses his ultimate move, Rocket Charge, to tells Koichi to jump off the bus as he tries to catch him, but fails. Koichi makes up with his force of will, allowing him to jump in midair. Ingenium has a hold of Makoto as both Quirk users were able to land on the other side of the expressway, safe and sound. Back to Koichi’s penthouse, Shoko states she has enough trust with the people she met and is heading home.