The stage is set at the Kugigaoka Magic School, which trains heroes. The homeroom teacher of the "Class 3-E," a class of underachieving students each burdened with some kind of bug, is none other than the Demon King!? To defeat the Demon King "Koro-sensei," who has gained abnormal speed due to a bug and is incredibly hard to hit, the students plot to bring the genius magic swordsman known as the "Red Devil," Akabane Karma, into their class...? Their weapons are swords and magic! The new adventure of Koro-sensei and his students begins now!