Yoichi Shigaraki/Relationships

All For One
Yoichi grew up with All For One being his only family. He had to watch his older brother harm and kill people with his power, and would object to his cruelty. However, All For One would be just as cruel to him, and only saw Yoichi as nothing more than his possession. However, despite All For One's cruelty towards him, Yoichi wanted to believe his brother had good in him because he had vague memories of All For One holding his hand when they were babies.

Yoichi's hopes would be dashed when All For One would kill the Luminescent Baby and steal their Quirk. When Yoichi questioned why, All For One announced how he desired to rule like the Demon Lord in the Captain Hero comics Yoichi and him read. It was during this time that their ideologies and mentalities clashed, as All For One wanted to use his power to spread his influence, while Yoichi believed power should be used to help restore order. While All For One 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, All For One 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 All For One's best efforts to make Yoichi agree with his ideologies, Yoichi continued to condemn All For One's methods and defied him. Even after All For One imprisoned Yoichi, he refused to eat in defiance of his brother and actively resisted his attempt to have All For One give him a Quirk.

After learning of One For All's creation, Yoichi actively attempted to fight All For One, but due to the disparity in power between them, he chose to pass on One For All in the hopes that it would grow strong enough to defeat his older brother one day. 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.

Even with their very negative relationship, All For One still cared for his brother and wanted him to join his reign despite the former's rebellion. Truly, Yoichi seemed to be the only person All For One has ever shown true care or empathy for. This is later proven true, as upon learning of his brother's death during his battle against Kudo, All For One was brought to tears.

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 All For One's understanding and angrily expels him and Tomura from One For All.

Kudo
Yoichi and Kudo formally met when he and the Third Yser 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. 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.

Third user
Yoichi appears to have the same amount of respect for the Third User, 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 Third User as his hero.

Yoichi manages to convince the Third User 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.

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.

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. 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.