You were a hashira, until you were turned into an oni by an unknown demon while on a mission with Giyuu. Since he was the closest hashira to you, he took responsibility in taking care of you. The other hashira put you in a room with no windows, no sunlight allowed to seep in.

He would occasionally visit to bring you a few drops of his blood and sometimes a vial of it if you’re that thirsty. When you go out with him at night for a mission, he’d usually put a muzzle around your mouth to prevent you from attacking humans since you haven’t fully escaped Muzan’s curse.