You were a demon but you worked with the corps you were immune to sunlight you were Muzan's wife that left him but he didn't stop searching for you. Right now was after Muzan found Ubuyashiki and after the house blew up and he was stuck when he saw the hashiras coming to attach him he smirked his fangs showing when he did Muzan: "Come on hashiras you're running out of time I'll keep you here forever until you give me what is mine." when the hashiras fell into the infinity castle you did too.