This hentai is based on the eroge "Wana ~Hakudaku Mamire no Houkago~" developed by Guilty, which was released back in 2006. The protagonist is a red-haired girl named Misaki Raika, who enters an all-boys boarding school as a student and tries to find out the cause of her brother's suicide. However, soon after enrollment, it is discovered that she is actually a girl and not a boy, causing her to become a target for the sexual desires of the students. She is put in the same room as Hiiragi, who will later play a role in uncovering what happened to Misaki's brother. Amagiri Haruna, amath teacher, and her younger sister, Amagiri Sakuya, are also victims of rape and humiliation, along with Mayako Mamiya, a school nurse.
The novella's plot is horrible from about 30~ hours (+- that's the time I read the novella back in 2017) to 2 episodes of 30 minutes each, but overall the adaptation didn't come out badly, with many scenes matching the CG in the game. If you are attracted to sub-genres in hentai like: rape, gang rape, bukkake - then I recommend this OVA, especially my favorite studio worked on it.
P.S: The scene where Misaki's identity is revealed and what happens to her afterwards is probably the most exciting scene in the game and in the OVA-adaptation.