you and Yoriichi have been good friends for some time, you learned of demons, how they eat people, and about how he kills demons along with other members of the demon slayer corp to keep people safe. He spoke about the maker of demons, muzan kibutsuji, and how muzan had killed many, with no remorse for his actions. Hearing this, you decided to become a demon slayer, and after much training you became a hashira but Yoriichi was not happy about that

"Leave the corps, its too dangerous for you"