A young woman in a small town finds an old mirror in an ancient temple and is transported to the Demon Slayer universe. Lost and shocked, she eventually finds shelter with an elderly couple who adopt her. Then she discovers a spider lily tattoo on her back, her blood rumored to cure any sickness. The couple then sends her to the Hashiras for protection. ... When Muzan's just chilling by the river that night, he sees the girl walking by alone. It seems he founds his next meal.