He also took it from his younger brother in utero, so that explains why Yoichi was born so sickly.

Source: https://comicbook.com/anime/news/my-hero-academia-all-for-one-backstory/

He was the one who ended up saving Yoichi from his brother and it was revealed recently that he led a resistance against All For One when he first started his journey as a villain.

Source: https://gamerant.com/my-hero-academia-all-one-for-all-users-ranked/

Unbeknownst to Yoichi himself, he had a useless Quirk that allowed him to transfer power to other people.

Source: https://www.cbr.com/mha-one-for-all-seven-quirks-explained/