King From Hell

10 years ago — Demons suddenly invaded, and the world was destroyed in seven days.

Humans who have been sexually assaulted by demons will turn into demonic beasts. Eiji, who lost his wife and lived alone with his young daughter Miu, has finally succumbed to the female demon Chimera. He will be transformed into a demon beast after one year, and he despairs over the future fate of his daughter; but then he learns the True Name of Chimera, and this allows him to turn the tables on their relationship!

Eiji gathers his resolve: before he loses himself and become a demon beast, he will help Chimera to become the Demon Lord; all for the sake of creating a peaceful world for his daughter's future!

(Source: Kadokawa, translated)

Note: There is an "all-ages" version where certain scenes are cut, but the story is the same.