Ichirou Satou is an ordinary high school student who pretended that he was a hero by the name of "Maryuuin Kouga" back in middle school, which led to others frequently bullying him. Now that he has left this embarrassing phase behind, he does his best to avoid standing out and live a peaceful life, although he feels the world has become quite dull. But when he makes his way back to school one night to grab a textbook he left in class, he runs into a strange girl wearing a costume.