Kudo/Synopsis

History
Kudo lived in the harshest era of Meta Abilities, when All For One's powers were reaching its peak with his control unchecked. Kudo had foreseen the terrible future All For One will bring upon as he expanded his influence to society. To counteract this, he gathered allies, and formed a resistance to oppose All For One and his new world order. While he had no direct confrontation with this resistance, All For One allowed his growing number of subordinates to deal with him and the resistance later.

One day, Kudo and his companion, the future Third User, raid All For One's base with the intention of killing Yoichi Shigaraki, his younger brother, for being associated with his enemy. However, as he and the future Third User enter Yoichi's imprisonment, he hesitates, decides against his initial assassination attempt and instead lends out a hand to Yoichi, rescuing him and inadvertently allowing his Quirk, One For All, to grow.

After being freed by Kudo, Yoichi was not strong enough to defeat his brother even with his new Quirk and too weak to even keep on living, so he passed it on to Kudo and the next generation in the hopes that one day One For All would be strong enough to defeat his older brother. Some time after passing down One For All, Yoichi dies. All For One tracked down Kudo to reclaim his brother, massacring the entire resistance, leaving only Kudo standing to oppose him. Even with One For All, Kudo wasn't strong enough to defeat All For One; however, by this point he had already passed it down to the Third User, while Kudo presumably brought time for his successor to escape

Kudo was fatally wounded in combat, and was being held by the throat by All For One. Kudo asked if All For One came to look for his brother, and he responded that Yoichi is dead and he was the one who killed him. All For One, with tears flowing from his eyes in despair and anger, began to choke the life out of Kudo, easily stopping a bullet shot at him from behind using his Meta Ability, Gearshift. All For One eventually kills Kudo, all the while in his final moments, he simply smiles at the Villain in satisfaction.

U.A. Sports Festival Arc
During the fight between Izuku Midoriya and Hitoshi Shinso in the tournament of the U.A. Sports Festival, Izuku is brainwashed by Hitoshi's Quirk, who orders him to walk out of bounds. Although Izuku tries to resist, he cannot disobey the order, but when he is about to cross the edge of the ring, Kudo and the rest of the previous users appear to Izuku as shadowed mental figures. They uncloud his mind and allow Izuku to use One For All in his fingers, allowing him to escape the trance and win the fight.

Pro Hero Arc
After an extensive day of One For All training, Izuku returns to Heights Alliance where he falls asleep immediately, experiencing a dream where he sees the previous users of One For All, recognizing them as the vestiges he had seen at the U.A. Sports Festival. However, unlike the others, Kudo and the Third User only appear as vague silhouettes, due to doubting Izuku as a capable successor and keeping their presence muted. Izuku proceeds to view a series of past events regarding Yoichi and All For One that led to the creation of One For All. Izuku wakes up after involuntarily activating One For All, damaging his room.

My Hero Academia: Heroes: Rising
During a devastating battle between a villain with a copy of All For One's Quirk, in a last-ditch effort to defeat him, Izuku transfers One For All to Katsuki Bakugo, even at the cost of rendering himself Quirkless once more. Through the dual power of the One For All's, the two manage to take the villain down, even as the remaining embers of One For All seemingly disappear from Izuku. However, the users of One For All, wanting Izuku to continue to harness the power, and recognizing his heroism of being willing to sacrifice his power to save everyone, only temporarily transferred the power over to Katsuki, while the full essence of One For All remains within Izuku. All Might tearfully thanks his master and predecessors for staying with Izuku.

Paranormal Liberation War Arc
In the aftermath of the Paranormal Liberation War, when Izuku is rendered comatose, he speaks to all the vestiges within One For All. The deceased users revealed that a vessel with an existing Quirk could not receive One For All without it warping and spilling over, and attempting to force it results in a shortened lifespan, like what happened with Hikage Shinomori, and that All Might managed to hold onto One For All for forty years because it perfectly fit his previously empty vessel, and became his Quirk.

They conclude that due to these circumstances, the true value of the power can only be wielded by those who lacked power to begin with, with Izuku following up that especially now that the previous user's Quirks have started manifesting, One For All must be carefully given due to Quirkless individuals slowly disappearing over each generation, so it was fate that Izuku managed to be the one who was bestowed the power. Because of this, Izuku is the last successor of One For All. Nana Shimura asks Izuku if he can kill Tomura, clarifying it isn't a request, but a question of his resolve. She reminds him of their last interaction and that since all of the inheritor's are connected to his emotions, they could telepathically sense that he saw him as someone who needed saving.

Izuku voices his opinion that countless people died and many of his precious friends were hurt because of Tomura, but he stands his ground believing that One For All is a Quirk meant to save lives, not kill; that All Might taught him that, and that he and all the other users who have helped grow and cultivate the power, have in the process saved and brought hope to countless people. He accepts the real possibility that Tomura can only be stopped by killing him, and he doesn't know how he will deal with everything exactly yet, but he still wants to try and save "that little boy", all the while briefly transforming into his child self. After the other users agreed to lend their full support to Izuku, Yoichi turned around to Kudo and the Third User, asking them to cooperate with their successor.

Kudo and the Third User initially refuse to even give Izuku a hand since he doesn't know what it means to wield such power that can stand up against All For One. The Third User reminds Yoichi how they lived during the worst era in their history, when All For One's control was spreading to its peak, and that it was their leader, Kudo, who did everything he could to strike back against All For One's control, including gathering allies to fight. Kudo talks to Yoichi about how many lives he took in order to bring down All For One, and that he can't devote their efforts to a boy who wants to "save" their mortal enemy, calling it a ridiculous delusion.

In response Yoichi asks Kudo and the Third User why they saved him despite their initial plan to kill him due to his ties to their "enemy" when they found him. He tells Kudo that had he not taken him out of that room, their fight with All For One would never have started. He also reminds Kudo that working with Izuku is their only choice, hence why all of them are here now. Kudo asks again if Izuku will be able to bring an end to the war with All For One, which Yoichi reassures, saying that it was because he reached out to save him that One For All was truly born. Convinced of Izuku's strong will and Yoichi's words of wisdom, Kudo and the Third User turn back toward Izuku with all the users on his side backing him up.

Dark Hero Arc
Izuku decides that, in order to protect his friends and loved ones, he will leave U.A. and act as bait to lure Tomura and All For One out of hiding, intending to fight and defeat them. Unfortunately, the searching proves fruitless, as the physical and mental stress begin to wear at Izuku, turning him into a ferocious looking creature that refuses to stop moving. He heads off on his own, ignoring the words and advice from the other Heroes to take a break. This causes the other users of One For All to tell him not to push himself since his wounds haven't fully healed yet, but Izuku still doesn't listen, using Danger Sense as an excuse to head out towards the next threat.

Within the vestige world, Nana fears her feelings are affecting Izuku heavily, but Daigoro Banjo states that for Izuku, every cause is a worthy cause. Hikage adds that for better or worse, awakening all of their Quirks enables him to act according to his primary motivation, to save everyone as a true superhero. Kudo says he is doing the right thing by pushing on without rest, because in this peculiar situation, that is the responsibility of the bearer of One For All and everyone's wills. He does, however, suggest something to bolster him; the support of his classmates that can help him carry the burden.

Final War Arc
With the number of Heroes dwindling rapidly, those that remain have come together to defeat All For One and his army of villains in the all-out Final War. They successfully lure All For One and his forces out of hiding, and manage to warp the villains to separate locations so they can be fought individually. Izuku is planned to face off against Tomura within a now floating U.A. High, which has been specifically designed to keep him contained. However, Izuku is caught off guard by an intervention by Himiko Toga, and warped to Okuto Island instead. With them unable to warp him back, he must make it there himself, which he does by combining Float, Fa Jin, and Air Force to fly across the ocean.

After leaving Okuto Island, Kudo appears to Izuku, after he tried to use his Meta Ability to get to U.A. faster. He reminds Izuku that his Meta Ability is only to be used as a "last resort" as it has transformed into a "unique power" due to the power that has been stockpiled in One For All over the generations. He tells Izuku that he should not become desperate and to have faith in his friends, as they are all out fighting for their own reasons and, with that in mind, he should focus on his fight.

Shortly afterwards, American fighter jets arrive to escort Izuku back to U.A., as he uses Blackwhip to swing across them, reaching the battlefield and joining the fight against Tomura. Izuku has a freak-out upon seeing all his barely conscious allies, but is able to calm himself down, asking "All For One" if Tomura is still within.

He claims that Tomura no longer exists, as he and All For One's minds have fully melded into a complete being. However, Mirio Togata reveals that during his battle, "Tomura" had an outburst at him, almost like as if he was a child. Realizing that the essence of "Tenko" still resided within their body, further uncovered by Nana noticing the faces of the Shimura Family on the transformed "Tomura"'s hand, they know that he's still in there.

"Tomura" attempts to fight Izuku, but Izuku ensnares him with Blackchain before throwing him into a obstacle. Once he has some distance, Izuku concentrates to himself, and Kudo appears before him, telling Izuku to make it quick, because once he starts using his Quirk, they need to finish him off in five minutes or the world is doomed. With nothing to lose, Izuku uses the Second's Quirk, Gearshift, to power his new Ultimate Move, Transmission, wherein, in the blink of an eye, Izuku appears under "Tomura", pulverizing him with consecutive punches in Second Gear, Third Gear, and finally Top Gear, and sending him flying upward.

"Tomura" is completely caught off guard by the attack, thanks to the Quirk's ability to let the user shift change the target's speed when touched. Kudo tells him that this Quirk is a different beast than before his last encounter since it has melded with One For All. Izuku goes into Overdrive, turning his 100% power into 120%. Kudo and Yoichi appear before All For One as the younger brother declares to him that today is the day they finally bring a end to their fight, as Izuku unleashes a fully powered Detroit Smash directly into "Tomura"'s stomach.

Thanks to Gearshift's significantly increased power, Izuku is able to greatly enhance his speed, and unleashes a Detroit Smash: Quintuple at "Tomura", revving around the arena too quickly for him to defend. The villain tries to predict where his next attack will be, but at the last moment, Izuku shifts into Low Gear, causing "Tomura" to miss the swing. Kudo states that the Quirk can now adjust speed while ignoring the laws of inertia.

"Tomura" attempts to counter, but Izuku uses Danger Sense to detect the threat, and immediately block his vision with Smokescreen. He then uses Float to quickly rise into the air, restraining and reeling "Tomura" up with Blackwhip, preparing to combine the power stored up thanks to the Quintuple attack with Fa Jin, executing another blast of Overdrive with Gearshift, unleashing the full might of One For All, pounding "Tomura" with his ultimate smash, breaking many of his fingers apart. As "Tomura's" body falls with a gaping hole in his chest, Kudo addresses to All For One that their Meta Abilities were never what he should've been worried about, rather he should fear the reason why someone chooses to use their gifts; true power lies in an individual's intent, which is why people call them "Quirks".

While the last attack destroyed Tomura's defense Form, Kurogiri suddenly appears and teleports Himiko's Twice Doubles all over U.A., undoing Erasure, and causing Tomura's body to explode and destroy U.A. Izuku is unable to move and needs time to recover due to the drawback of the powered-up Gearshift took a toll to his body, as when his cells don't get a moment to rest, his body can't get enough oxygen and risk breaking down.

Kudo reminds him he can't fall yet, however, he continues that there is a silver lining, as thanks to One For All and All For One resonating with each other, they can see "inside" each other, and can see All For One currently unable to manipulate Tomura's body. He tells Izuku to do whatever to make his body act, as the chain of events leading to this moment will be his power. With Tomura regaining full control of his body, and Izuku able to move again, he tackles Tomura outside of U.A., where they proceed to battle on the ground.

As Izuku and Tomura fought to a stalemate, All For One eventually carries a battered All Might after defeating him in brutal fight where he can show the world he has failed them and prepares to kill him in front of the live broadcast for the whole world to see. As All For One is ready to rip All Might apart in front of everyone, Katsuki Bakugo appears from above U.A., and realizing what he is about to do Izuku reaches his arm out, grabbing Katsuki, and the three begin to twist.

Kudo realizes what Izuku is trying to do and calls out to him, warning him about using Gearshift again as it will cause the recoil blowback to hit harder on him, and must only be after he's found the assured path to success. However, seeing the disappearing All Might vestige within One For All, Izuku goes all-out and uses Gearshift in conjunction with Katsuki's Cluster and throws him over, sending Katsuki barrelling through the skies at insanely, blistering speeds. In spite of that, within mere seconds, Katsuki defies fate and successfully steals back All Might from All For One's hands. The vestige within One For All suddenly turns back into a spirit, surprising Izuku and Kudo, as Katsuki yells out that they're going to win.

Izuku proceeds to use Gearshift on himself for one last time to finish the fight against Tomura, knowing that the blowback will be enough to take him out of the fight for good.