Sadan Academy is infamous for its brutal discipline, where students' screams never cease. Into this terrifying school emerges a warrior fighting for justice. Concealing her face yet baring her body, the beautiful and fearsome heroine Moretsu Mask makes her appearance, punishing corrupt teachers and shattering the school's twisted order. In response, the principal develops a robotic teacher, Tetsujin 28-eimon, to uncover her true identity, while suspecting the lovely female teacher, Natsuki Hotaru, of being Moretsu Mask and subjecting her to intense torture. To save Natsuki-sensei, Moretsu Mask reappears—but she is defeated in battle against Tetsujin 28-eimon. The war between justice and evil escalates into deeper, darker conflict.