Saizou seems to be a typical student, but he’s actually a ninja-in-training! Maybe destiny had something to do with it, but he met four girls who also had secrets which couldn’t be told to others. They were the blonde transfer student Himeria (who’s actually a princess), his model-like senpai Yuuki (who’s actually a heroine of justice), the beautiful swordsman Hijiri (who’s actually a girl in disguise), and his small kouhai Koharu (who has superhuman strength in certain situations). Himeria revived the local history research group, which became the ‘secret union’.