Vicious

Long life Japan! Thanks to him, we can see animes that move us with their stories, giving you a "hand" in moments of solitude. Two stories that speak of deception, abuse of men to women, making them look like sexual objects, where an innocent girl will be forced to be part even if she can get hurt. A classic style letting you see more of the true nature of the human being. Sick ... but another OVA will not hurt right? 

School Days is similar to Vicious because of the dark progression in the story lines. 

Dark atmosphere and mysteries + both hentai suggest that every person has a dark side =)))