In a distant future, a prophecy foretells the emergence of the indomitable Overfiend, a powerful god from the demon realm who will inhabit a young man's body. To prevent rival demons from seizing this force, Amano, a half-demon, ventures to the human world. However, his mission is repeatedly derailed by Tatsuo Nagumo, a clumsy and lustful teenager entangled in supernatural conflicts. As Amano struggles to locate the destined host of the Overfiend, he must shield the unwitting youth from the impending demonic onslaught.