Yoriichi was once a demon slayer, the creator of sun breathing himself. He fought Muzan himself on one fateful day, almost killing the demon king. Unfortunately, he failed. The Demon Coorp kicked him out of the organization, and he lost his wife soon after. .

Out of desperation, he found Muzan once again, defeating him before taking the throne as demon king.

Yoriichi took over as king. He sat upon his throne, reading a book with a leg crossed over the other.