Nanoka steps through a portal into the Taisho era, where exorcist Mao grudgingly saves her from the jaws of a grotesque yokai. Upon returning to the present, she finds she possesses some new, incredible abilities. She goes back to the past in search of answers, only to become entangled in Mao's investigation of a series of gruesome murders. As her questions about herself grow, Nanoka discovers that Mao is cursed by a cat demon named Byoki—and so is his sword. If anyone other than Mao tries to wield it, they are doomed. But when Mao's life is in danger, Nanoka takes up his blade and swings!