After the events of the ''Sukeban Deka II'' TV series, the now 18 years old Yoko Godai (Yoko Minamino) has abandoned her special agent Saki Asamiya name to return to her normal life and is studying for college entrance exams. However, she accidentally bumps into a young man named Kazuo Hagiwara (Shinobu Sakagami) escaping from a group of hitmen, and learns that he comes from Sankou Gakuen, a private school located in a remote island known as Hell's Castle. The school is ruled by a former revolutionary leader thought to be dead named Hattori (Masato Ibu) who is trying to brainwash students into terrorists to help him stage a fascist coup d'etat in Japan. They are then attacked and captured in a bus driven by Sankou Gakuen henchmen, who proceed to submit Saki to electric torture, but they manage to escape.