Kuro no dansho

First, a word of warning - this thing is hentai. Keep that in mind. There is sex involved, although most of it's not exceedingly graphic.

A bigger issue for most folks will be the blood and similar issues - this thing features a number of very messy killings, with eye removal and skinning. Want to watch out for those, especially if you're eating at the time.

However, on the show itself, it's actually remarkably well-written. Particularly for the type of show it is. It's more mystery than porn in the first part, and more horror than either in the second, and it's well-done all around. The sex-scenes actually make sense (for the most part) rather than just being thrown in, with a couple fairly minor exceptions.

If you're looking for well-written adult anime with a horror/mystery bent, you won't go wrong with this one. If you're against sex and/or blood in your animated entertainment... stay well away.