Yuuko Yoshida, a high school girl, wakes up with demonic horns and a tail after having a bizarre dream about a mystery ancestor. Her mother, dazed and bewildered, confesses to her a terrible family secret: her ancestors are from the Dark Clan, who were exiled to live powerless and poor by their sworn foes, the magical girls of the Light Clan. Yuuko must find a magical girl, murder her, and spatter her blood all over her ancestor's Demon God statue in order to break their ancestors' curse. Fortunately for "Shadow Mistress Yuuko," she is saved from being driven over by an incoming vehicle by a supernatural girl. Momo Chiyoda, Yuuko's classmate at Sakuragaoka High School, is significantly older.