Kuro Ai: Hitoyozumakan Inkou Rannyuuroku

Tetsuya's investigation into a luxurious hotel turns over a nest of yakuza and a bizarre orgy cult. On rich silk sheets and velvet chairs, the rich and powerful participate in sex acts so depraved that just witnessing them is likely to turn a man into a monster. But the true purpose of this cult is a pact with evil energies that can literally turn Tetsuya into an inhuman demon.

(Source: Anime News Network)