Ririchiyo Shirakiin, a fifteen-year-old heiress with yokai blood and a habit of lashing out to hide her loneliness, moves into Maison de Ayakashi, a high-security apartment complex for Atavists, humans who can channel their supernatural ancestors' powers. Despite never requesting a bodyguard, she is assigned Soushi Miketsukami, a devoted nine-tailed fox spirit who pledges absolute loyalty to her from the moment they meet.