Every 3,000 years the realm of humans (Ninjinkai) is united with the realms of the demons (Makai) and the man-beasts (Juujinkai) by the revival of the Overfiend (the Choujin), the god of gods. The saga follows Amanojaku - a man-beast - and his quest to find the real Overfiend and to ensure the safe future of all three realms. However, he finds his beliefs put to the test when he encounters numerous Makai, who are out to destroy the Overfiend and prevent the three realms from joining.
The notion of animated sex is no longer an isolated, foreign concept, but it is still an area of anime with a lot of stigma attached to it. Hentai is often seen as taboo and a perversion, but its origins in history and how it developed from there is a story unto itself.