Hiiro no Koku
Genres: Hentai
Type: OVA, Episodes: 5
Aired: Sep 18, 1999 to Sep 15, 2000
Studio: Meltdown
Source: Manga
Rating: Rx - Hentai
Synopsis:
Based on the manga by Sanbun Kyouden.

A housewife gets raped by a bunch of men. As it turns out she likes it and her life becomes a succession of perverted sexual adventures. 

(Source: AniDB)