Kaigaku

Intro his selfish choice to abandon the other orphans he grew up with to save himself from a demon at Gyomei Himejima's temple, which led to the children's deaths and Gyomei's subsequent frame-up. This intense, life-long self-preservation drove him to become a coward and a traitor to his fellow Demon Slayers, ultimately leading him to accept Muzan Kibutsuji's blood and become a demon to survive an encounter with Kokushibo.