Based on the erotic game by Elf.

In the girls dormitory of Shukusei Music Academy are the famous daughters of good families. In the middle of the night, the girl's screams echo in the silent academy. Kaori is tied up and at that moment she becomes baptized into disgrace. There is a man whose name is Kato Shusaku who looks down at her with a fiendish grin as she cries in misery...

(Source: Anime News Network)