When the Devil King Lucifero announces his retirement and the need for a successor, the Devil King Cadets assemble to compete in the succession event in the human realm. Despite this significant event, the Devil King's descendant, Osamu, shows little enthusiasm for the contest, preferring his part-time gig at a convenience store over the fate of the world. Reluctantly, Osamu embarks on the task of gathering familiars known as 'Child,' which stem from human souls. While Osamu remains fixated on his mundane job, he lags behind the other Cadets in this crucial endeavor.