"DevilMan" tells the story of Akira Fudo, a high school student who is adopted into the Makimura family following the death of his parents. One day he secretly summoned by his best friend Ryo Asuka, whose own father disappeared during an expedition to the South Pole.
The elder Asuka was a professor who had tracked a new type of energy to an underground lake, only to discover that energy source was actually a host of demonic lifeforms that evolve by possessing the bodies of other beings.
The demons have escaped from their prison and launched a worldwide assault on mankind. Following a series of brutal killings by these creatures, human "demon hunters" attempt to save humanity by exterminating the beasts.
In the midst of this chaos, Ryo asks Akira to unite with the demon Amon; if successful Akira will possess the demon's power and be able to use it for good. Once merged with Amon, Akira's heart and strong will prevail and he is now able to transform into the "demonic human" named Devilman.
Akira now must fight alongside and against Ryo (who is revealed to be the reincarnation of Satan) and carry the heavy burden of protecting not only his beloved Miki Makimura, but the rest of the world as well. In the abyss of despair that may spell mankind's demise, Devilman alone must fight this sad battle to assure a future for humanity.....