A woman claiming to be the culprit visits detective Kajitani (Takeda Rina) from the investigation headquarters. Kajitani, who is pursuing a serial killer who has shocked the whole of Japan, warns her by saying, "If it's just a prank, I don't have time to bother with it," but the woman says, "I don't think there will be any more victims," ​​and hands her a notebook. After reading the notebook, Kajitani begins to talk as if looking back on the serial murders that occurred at Seiran Gakuen and its surrounding areas six years ago. The woman then reveals that there was a student who was fascinated by the suspect Kurokawa (Yamamura Ryuta), and that the person began committing small crimes at the school before eventually becoming a serial killer.