A long time ago, the Earth was ruled by demons. The demons constantly fought each other for survival, but soon found themselves fighting a new race of beings: the first humans. The demons then became imprisoned in ice after a great cataclysm. They would remain there until the ice melted, after which it was said Satan would rise and lead them in Armageddon.

Akira Fudo's best friend, Ryo Asuka, introduces him to this schocking truth, and asks for his help in his plan to save humanity: to borrow a devil's power and create a hybrid, a devilman who can protect humans from demons.