It doesn't get any more cult than this. Legend of the Overfiend is the poster child for anime sex and violence, putting the work of Kawajiri and others to shame. At least, if you seek out the uncut 3-part OAV rather than the sanitized movie version, which, when you do decide to watch this film, is definitely the way to go.
It's a film that feels right at home between franchises like Violence Jack and Devilman, but goes the extra mile to be as nasty as possible. While the manga was lighter in tone (with more high school comedy thrown in - only minor traces remain in the film), the anime puts all of its focus on the apocalyptic battle between the human and the demon worlds.
The animation is actually pretty decent, though the insane monster designs do help to neatly mask some cheaper bits. The mix of sex and violence is taken to its extreme so be warned, more surprisingly though Takayama still manages to get some actual plot in there that isn't half bad for this type of film. Crazy, violent and over-the-top, but one of the best in its genre.