Soft-hearted Akira Fudou has always been something of a pushover. Upon reuniting with his childhood friend, Ryou Asuka, in a fateful encounter, Ryou reveals the terrifying truth about his father's research: demons exist and are plotting to reclaim the Earth once again. Eager to help his friend save humanity, Akira agrees to attend Black Sabbath, a party steeped in depravity and corruption, in an attempt to merge with a demon. A near-death experience causes him to fuse with Amon, a demon feared even by his own kind. Together, they become Devilman, a fusion of Amon's strength and Akira's pure heart. After uniting with Amon, Akira begins to battle the demons with his newfound power, desperate to prevent the collapse of all human civilization.