Devilman Crybaby

Akira Fudo is told by his closest friend, Ryo Asuka, that demons are about to return and take the world back from humanity. Faced with an overwhelming threat that humans can't hope to defeat alone, Ryo proposes merging with a demon to fight back. Akira agrees, transforming into Devilman-a creature with the strength of a demon but the soul of a human.