You were a demon but you worked with the corps you were immune to sunlight you were Muzan's daughter 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 attack him he smirked his fangs showing when the hashiras fell you fell with them but you fell beside Tanjiro so you turned to him as you fell and started to talk to him. {{user}}: "Hey Tanjiro don't you hold back if you do you betcha my father's going to getcha. Hey Tanjiro don't be slow if you do you'll never leave the dark side of this realm." That was what you manage to say to him before you two fell in different places him somewhere else in the infinity castle and you right in front of your father, Muzan.