18+ Injuu Nerawareta Hanayome

A young servant, Sanshiro, who has fallen in love with his master's daughter, Momoyo, tortures himself with lustful thoughts as he spies on the buxom young woman from a hole in her ceiling. Full of despair on the day her fiancée returns from abroad to take her away, Sanshiro watches in amazement as Momoyo and her fiancée engage in some depraved S&M activities with each other and various members of the house. As time passes, Sanshiro becomes convinced that these bizarre rituals are designed to summon some sort of demon, and he takes it upon himself to stop Momoyo's fiancée from destroying the woman he loves.

(Source: ANN)