Ail Maniax: Inma Seifukugari & Majogari no Yoru ni

Both hentais that have quite a lot of guro and are very hardcore. The characters are well animated, and the animes themselves are very detailed, so you'll need to have a strong stomach to watch either of these. The music is very similar too. Plus, they're both by the same company so you get the same sort of vibe from them both. 

Both anime would go under the 'guro' genre, tons of hardcore scenes in both of these 

Both OVA series are some of the few hentai anime that can have the guro tag, extreme roleplay on both, plus there's some occult aspects thrown in the story. Ail Maniax is more hardcore, though.