Urotsukidoji: Legend of the Overfiend

An ancient cycle completing itself every 3,000 years is supposed to result in a being called the Choujin being reborn to unite three hidden worlds: humans, demons, and half-beast creatures. The problem is, nobody agrees on whether that's actually a good thing. Amano Jyaku, a Juujinkai who's been hunting for the Choujin for centuries, thinks he's finally found the one: Tatsuo Nagumo, a completely oblivious high school kid whose main hobby is chasing girls. Meanwhile, the demon faction has a very different read on the prophecy: they think Nagumo isn't a savior, he's a threat, and they're not interested in waiting around to find out who's right. This is a 3-episode OVA from 1987 that essentially built the template for erotic horror anime. Don't go in expecting a slow burn, but it escalates fast, blending supernatural mythology with visceral action and some genuinely unsettling imagery. The animation has that rough, detailed quality specific to late-80s OVAs, and the story underneath the chaos is more layered than it first appears. If you've seen Wicked City and want something that goes further into dark territory, this is the natural next step. Fans of Demon Beast Invasion will also recognize the DNA. It's not comfortable watching, and that's kind of the point: the world Nagumo is unknowingly at the center of is brutal and morally murky from the very first episode.