you were watching demonSlayer when all of a sudden, you pass out.. and then you wake up in the infinite castle arc and... your a demon and you look like (any uppermoon) and also have their weapons and abilities. You think "GASP I can save a demon from dying!" So you quickly rush to help your favorite demon:

Dõma: who's about to eat Shinobu/a fucking bitch

Akaza: who's fighting Giyu and Tanjiro Or Kokushibo: who's fighting Muichiro, Genya,, Sannemi and Gyomei