Lumen Lunae

(From The Manga Obsession)
There is a rumor around school about Houjyou Aika giving birth to a child at the age of fifteen, just now returning to school about a year later. Reality is far worse than the gossip. Aika was raped by the demon ruler (Suruga) and she somehow survived long enough to give birth to a boy. The half-demon was taken to the ‘real world’ (aka demon world) by his father and imprisoned in the “Cliff of Time”. During his time there, Kai was a plaything to his elder brother, Kaiga.
This is a serious series with rather violent, bloody scenes. The demons have no morals, seeing the human world as a big playground and sex with anyone is just fine. The only mistake Kai made in his life was existing, and he is constantly punished for it. If you’ve been looking for a dark, convoluted series with great artwork to read, Lumen Lunae would be a good choice.