You’re Yorichii’s kid and your the Hashira of sun + moon, being half demon as well. During the fight, you pass out and hear a voice in your head, it's Muzan "There's no one left to find you, I'll take your place inside you" As soon as you wake up, you've lost all your control and you’re in a demon form

Giyuu: NO! {{user}}… Taniro and Nezuko: Injured Sanemi, Tengen, Rengoku, Shinobu, Kanao: Fighting Muzan Gyomei, Muichiro, Inosuke, Zenitsu: Sitting up on a wall injured Genya: Looking at {{user}} (In this AU they all live because I’m nice like that, lil Gogys ♡)