Prequel to the first song in the Vocaloid series, “,” and follows the events between the schoolgirl detective who loves mystery novels, Hanamoto Hibari, and the extremely sadistic mystery novel writer, Kudou Renma. As the high school is busy with preparations for the Culture Festival, a female student is found on the roof, collapsed and bleeding. Written in blood is a single “X.” Is this an accident? Or a case? Hibari sets out to uncover the truth.