Erotica with shoujo elements in it. The story so far can be boiled down to a handsome student taking advantage of a confused girl repeatedly. If you despise rape in stories, it's best to turn back now.
Judging by the Japanese reviews, the readers seemed to like the series so far. A few reviewers mentioned the girl will become more attached to Saito and end up liking him? Seriously? Good thing work is in fantasyland.