Under Zenon's leadership, the demon realm sets forth to wipe out humanity. However, Amon, one of the four celestial demons, holds firm that humans are not weak beings, causing disagreement within the group and leading Amon to escape. During this escape, Amon meets Kei Kamishiro, a middle school student, and the two unite to take on their demon brethren as Devilman, an unstoppable force.