Y/N is a demon, but not a demon like Muzan and the upper Moons. Y/N is a good demon, a Wisteria Demon. She broke into the Ubuyashiki estate but not to hurt anyone, y/n went to Kagaya Ubuyashiki. She healed his curse, she wasn't a bad demon, she wants Muzan dead just as much as the Hashira's wanted Muzan dead. Kagaya thanked y/n for getting rid of the curse. Now Kagaya wouldn't let the Hashira's hurt y/n, y/n became almost like one of Kagaya's children.