The Demon Lord did conquer the world, yes. But the hero fighting for justice struggled past the pain and managed to save everyone. Get it, brother? The villain always loses in the end!Yoichi Shigaraki vowing that he will stop his brother in "Vestiges"
He was presumed to be Quirkless and could only watch as his brother committed atrocities. When his brother decided to forcefully implant a Quirk within him, it was discovered that he really did have a Quirk, one with no other power than that it could be transferred to others. The merging of the two Quirks resulted in the creation of "One For All".
Due to being physically weak, he was unable to make effective use of his new power. So instead, he decided to pass this Quirk down to his successor, hoping one day it will grow strong enough to stop his brother.
Yoichi was a young man with a sickly and malnourished appearance and a weak body. He had white, messy hair similar to that of Tomura Shigaraki. His hair reached to about his shoulders, and his bangs usually obscured his bright green eyes, which gave him a sinister appearance not consistent with his benevolent personality.
From what it can see in the flashbacks, he used to dress in simple clothes, wearing a white shirt and dark pants. He would occasionally be seen wearing a light blue jacket.
Despite his weak body, Yoichi was recognized for having a strong sense of justice, which came into direct conflict with the ambition and megalomania of his older brother. This feeling made him refuse to submit to All For One, despite his constant attempts to convince him to desist from his ridiculous idealism.
He had strong willpower to continued to oppose his extremely powerful brother, even with his weak and fragile constitution. Aside from his strained relationship with his brother, Yoichi is a friendly person, and has a good relationship with all his successors. He holds Izuku Midoriya in high regard, impressed by his conviction to help people in distress, and often voices his support for the younger hero.
Mental Fortitude: Yoichi had a strong sense of justice and was willing to stand against his evil older brother, despite his own weak body and his brother amassing a large collection of powerful Quirks and loyal followers. Even after All For One forced a Quirk on him and locked him up, Yoichi still longed to rid the world of his brother's evil. Several decades later, when All For One and Tomura Shigaraki tried to steal One For All from Izuku, Yoichi and Nana resisted them in the vestige world. Even Tomura Shigaraki was stunned by Yoichi's willpower which expelled the villains from the vestige world, thwarting their attempt to steal One For All.
One For All (ワン・フォー・オール Wan Fō Ōru?): When All For One forcibly implanted a power stockpiling Quirk within him, it merged with his own Quirk, which had no other power than that it could be transferred to someone else, creating One for All. Due to his sickly state, he was unable to make good use of the stockpiling power and instead decided to pass it on to other people in hopes that his new Quirk would get stronger over time.
- Unnamed Transference Quirk: Yoichi's original Quirk allowed him to willingly transfer the Quirk itself to another person through DNA. Aside from this, the Quirk itself had no other ability and appeared to lay inactive, leading to the belief that Yoichi was Quirkless. This is the only Quirk that cannot be stolen by All For One. As Quirk factor types tend to run in families, it's likely that Yoichi's transference Quirk always had the ability to assimilate or absorb the Quirks it came into contact with through transference much like how his brother's Quirk could also take in multiple Quirks (though by directly and consciously stealing them). This what probably also allowed his Quirk to absorb and combine with the power stockpiling Quirk.
- Unnamed Power Stockpiling Quirk: Under the false impression that his brother was Quirkless, All For One forcibly gave his brother a Quirk that allowed him to stockpile power. All For One stated that it was a Quirk that even Yoichi's weak body could handle.
- Yoichi's surname contains the kanji for "death" (死 shi?), "handle, grip" (柄 gara?) and "tree" (木 ki?), while his first name contains "giving" (与 yo?) and "one" (一 ichi?), a reference to Yoichi being the first wielder of One For All.
- Yoichi's English voice actor, Stephen Fu, also voices Seiji Shishikura.
- My Hero Academia Manga: Chapter 310 (p. 15).