Devilman

A journey through the Himalayas ends in death for teenager Akira Fudou and his father when demons strike. A powerful warrior of the Demon Tribe then takes Akira's body as a disguise, entering human society under orders to help prepare Earth for an invasion.

The plan unravels after Devilman encounters Miki Makimura, the girl who was dear to Akira, and develops feelings strong enough to turn him against his own kind. Choosing to defend Miki and humanity, he becomes a traitor in the eyes of the Demon Tribe, drawing the wrath of Zennon and a succession of increasingly dangerous demons sent to destroy him.