Yoichi Shigaraki/Relationships

All For One
When they were young, Yoichi and All For One appeared to have a good relationship, as they would read the same comic books together. However, their relationship became strained with the introduction of Quirks and the Quirk All For One possessed. 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.

Despite All For One's best efforts to make Yoichi agree with his ideologies, Yoichi condemned 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.

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.

Second user
Yoichi and the second user formally met when him and the third user broke into his prison vault. As the second user led a resistance against All For One, they initially planned to assassinate Yoichi for his connection to the villain. The second user 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 the second user for rescuing him, going so far as to call him his hero. Because of this, Yoichi chose the second user to inherit One For All and fight against All For One.

When the second user was refusing 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 the second user who chose to help Yoichi, in spite of knowing that he was related to his mortal enemy. Yoichi then manages to convince the second user 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 the second user 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.