"Mix with the devils, rob the devils of their power... With these hands, I will create a new Demon King for their destruction!"

10 years ago — Devils appeared all of a sudden, and the world was destroyed in 7 days.

Humans who have been sexually assaulted by devils will turn into demon beasts. Eiji, who lost his wife and lived alone with his very young daughter Miu, has also finally fallen victim and became the subordinate kin of a female devil, who is a chimera. He will turn into a demon beast after 1 year, and so he despairs over his fate of becoming separated from his daughter; but then he learns the True Name of the chimera, and this allows him to turn the tables on their master-servant relationship!

Eiji gathers his resolve: before he completely turns into a demon beast, he will raise this chimera to become the Demon King; all for the sake of creating a peaceful world for his daughter to live in!

(Source: Kadokawa)

Note: this has an "all-ages" version where certain scenes are cut, but the story is the same. Tatesc publishes the full, uncut version.