In a world where demons reign supreme with unmatched power, humans are helpless against their might. Ryo Asuka devises a daring scheme to empower his kind-hearted friend, Akira Fudo, by allowing him to be inhabited by a demon. Believing in the theory that a pure-hearted individual can tame the demon within, Akira becomes the vessel for the formidable demon, Amon. As chaos ensues in a nightclub, Akira successfully merges with Amon, becoming humanity's beacon of hope in the eternal battle against the malevolent forces that have haunted mankind for centuries.