When he was in the third year of middle school, Hizaki Shiou was summoned to another world to save it. After defeating the Demon King, he was forcibly returned back to the present day. Yet another three years later, he is summoned to the other world once again, this time to stop the rampage of the secret society "Helheim." That organization was supposedly actually the one that he had founded during his chuunibyou phase, where he called himself the "Corpse King"—a dark past too embarrassing to remember!