Family#
Zen Shigaraki#
Yoichi grew up with Zen being his only family, who named him "Yoichi" because he was his first possession in this world.[1] He had to watch his older brother harm and kill people with his power, and would object to his cruelty. However, Zen would be just as cruel to him, and only saw Yoichi as nothing more than his possession. Despite Zen’s cruelty towards him, Yoichi wanted to believe his brother had good in him because he had vague memories of Zen holding his hand when they were babies.
Yoichi's hopes would be dashed when Zen killed the Luminescent Baby and stole their Quirk. When Yoichi questioned why, Zen announced how he desired to rule like the Demon Lord in the Captain Hero comics they used to read.[2] It was during this time that their ideologies and mentalities clashed, as Zen wanted to use his power to spread his influence, while Yoichi believed power should be used to help restore order. While Zen claimed that he was doing just that, Yoichi saw through his schemes of gathering people so he could use them for his own purposes, only to dispose of them eventually. In turn, Zen mocked Yoichi for his weak body and for seemingly being Quirkless, but despite the disparity in their power, Yoichi still tried to stand against his brother's tyranny. Despite Zen's best efforts to make Yoichi agree with his ideologies, Yoichi continued to condemn Zen's methods and defied him. Even after Zen imprisoned Yoichi, he refused to eat in defiance of his brother and actively resisted his attempt to give him a a Quirk.
While Yoichi became fully aware of his brother's true compassionless nature and how he only viewed people as playthings to use for his own amusement, he still grieved over how Zen turned out, saying that the ability to give and take could have been the kindest, most charitable power in the whole world.[1] After One For All's creation, Yoichi escaped from confinement with the help of Kudo and Bruce. However, All For One caught Yoichi after two months and killed him. Zen named his brother Yoichi because the latter was his first possession in this world.[3] When Kudo reminded All For One about Yoichi's death, the villain shed crocodile tears to confuse him.[4]
One century later, the two brothers meet in the realm of Vestiges when All For One attempted to steal One For All from Izuku. All For One derides Izuku's ability and rebukes his brother for choosing to stay with him. Yoichi retorts that Izuku's commitment to heroism is beyond Zen's understanding and angrily expels him and Tomura from One For All. Yoichi seemed to have had no qualms over wanting his brother dead if it brought peace to the world and ended his tyranny for good. During the Final War and Deku’s battle against "Tomura" on U.A.'s Flying Fortress, Yoichi confronted Zen, telling him that today will be the day they finally end their long battle.[5]
Even after witnessing his brother's defeat at the hands of Katsuki Bakugo, Yoichi expressed no happiness or relief at the sight of Zen's downfall, and only watched with a somber expression.[6] In the end, at the face of Zen's final defeat, due to Midoriya, a small ember of Yoichi's vestige remained to meet Zen's vestige. Yoichi apologizes for failing to lead his brother down the right path and tells him that Izuku is allowing both of them to rest. As his brother begs to see Yoichi one last time, Yoichi claims he cannot, implying he would have if he could. However, despite being willing to stay with his brother as they both vanish, he states now was the time for Zen to pay for exploiting everything for himself. Izuku, Tomura, and most of the other One For All vestiges then rush at them at once and smash their Quirk Factors together, erasing both of them for good.
Successors#
Toshitsugu Kudo#
Yoichi and Kudo formally met when he and the Third User broke into his prison vault. As Kudo led a resistance against All For One, they initially planned to assassinate Yoichi for his connection to the villain. Kudo nearly went through with it, but had a change of heart and chose to rescue him instead, offering his hand to Yoichi, who accepted. He was incredibly grateful to Kudo for rescuing him, going so far as to call him his hero.[7] Because of this, Yoichi chose Kudo to inherit One For All and fight against All For One.
When Kudo refused to help Izuku due to believing his ideals of wanting to save Tomura Shigaraki to be foolish, Yoichi was the one who reminded him that it was Kudo who chose to help Yoichi, in spite of knowing that he was related to his mortal enemy. Yoichi then manages to convince Kudo to lend Izuku his aid to fully master One For All.
Bruce Lee#
Yoichi appears to have the same amount of respect for Bruce, since he fought alongside Kudo and helped break Yoichi out of his confinement when the plan changed from killing Yoichi to rescuing him. He also refers to the latter as his hero.[7]
Yoichi manages to convince Bruce to give his support to Izuku to help fully utilize One For All.
Izuku Midoriya#
Yoichi formally meets Izuku in a dream, where he shows Izuku his history with his older brother and what led to the creation of One For All. Yoichi is able to recognize Izuku as the Ninth User of One For All, warning him that they've passed the singularity point for One For All, but assures him that Izuku will receive help.[3]
Yoichi meets Izuku again in the mental world when All For One is attempting to steal One For All from Izuku. When All For One derides Izuku for giving in to blind anger and his inability to protect any of his allies, Yoichi defends him by saying Izuku is driven by a desire to help others unlike anyone else, declaring that they will stay with Izuku and expelling All For One from the mental mindscape.[8]
Yoichi sits with the rest of the One For All users when Izuku is rendered comatose. He explains to Izuku the growing power of One For All that allowed the vestiges stored inside to loosely communicate with Izuku, until All For One's attempt to steal One For All pulled the vestiges out and allowed them to fully interact with Izuku. He also explains how Toshinori Yagi was able to hold One For All for so long due to being Quirkless and how he was able to imbue a true piece of his consciousness inside of One For All.[9] Along with Nana Shimura, he questions Izuku's resolve to eliminate Tomura, having sensed his doubt and compassion for Tomura in the mental mindscape. However, when Izuku expresses his resolve to try and save Tomura, Yoichi happily smiles and expresses pride in knowing that Izuku holds One For All.[10]