Devilman Crybaby

Akira Fudou learns from his best friend Ryo Asuka that an ancient race of demons has returned and intends to reclaim the world from humanity. Ryo believes humans cannot defeat them through ordinary means and proposes a dangerous solution: Akira should merge with a demon and take its supernatural power for himself.

The attempt succeeds, transforming Akira into Devilman. He retains a human soul while gaining a demon's abilities, placing him between the two sides of the conflict. Devilman Crybaby begins with that transformation and follows Akira into a battle against the returning demons, as the power meant to help him fight them fundamentally changes the terms of his life.