Having defeated countless enemies, obtaining wealth, fame, and everything else imaginable, the most powerful king, Grey, abruptly dies one day. He then awakens suddenly, having reincarnated in a world where magic exists. He is given the name Arthur, and begins living a second life, with loving parents.

The Leywin family travels to the floating city of Xyrus so that Arthur can begin his formal education in magic. The adventuring party that Reynolds and Alice belong to, the Twin Horns, accompany them as guards, when they run into something unexpected...