Nanoka's life is completely turned upside down when she is suddenly transported through a portal to the Taisho era (ancient times). There, she meets an exorcist named Mao, who, though a bit arrogant, saves Nanoka from the clutches of a dangerous yokai. When Nanoka returns to her own time, she realizes that she now possesses some unique and powerful powers. She goes back to find answers to her questions, but there she becomes embroiled in the investigation of some strange and horrifying murders along with her mother. Nanoka discovers that her mother is possessed by a feline demon named Byoki—and not only her mother, but her sword is also cursed. The rule is that anyone other than her mother who touches the sword will be killed. But when her mother's life is in danger, Nanoka, without thinking, picks up the sword and attacks the enemy!