Neko-Musume is consulted by Mana after "strange things have been going on at school recently," and she visits Mana's school to investigate. One of the Seven School Mysteries, "Hanako of the Third Floor Girl's Bathroom," is Neko-Musume's friend, so the two set off to visit her. However, Hanako cannot be found. It's not only Hanako. Rumors of the Seven School Mysteries yōkai haven't been heard of these days, either. Sunakake-Babaa, Konaki-Jijii, and the others arrive after they lose contact of another School Mystery, Kinjirō Ninomiya. They all chase after a suspect and are led to the second floor boy's bathroom...!?