Fourteen-year-old Iruma Suzuki has the worst luck possible! Incapable of saying no to anyone, he has always performed whatever life-threatening jobs his greedy and lazy parents requested. His life takes an unexpected turn when they form a contract with Sullivan, a high-ranking demon, at the cost of his soul. Afraid and confused, Iruma is surprised that all Sullivan wants is to act as his grandfather.

Sullivan takes care of Iruma and decides to enroll him in the demon school Babyls. Iruma's greatest challenge is hiding his status as a human, so keeping a low profile among his peers is the only option. However, Iruma will soon discover that he is no ordinary human, and the demons might also be more than what meets the eye.