The Lickerish Stranger (2017)

Nagisa is living together with handsome college professor, Kotaro. However, lately Kotaro has been particularly violent towards Nagisa during sex, even going so far as to hurt her. One day, Etsuko, a woman claiming to be Kotaro's sister, appears at their house. Etsuko asks to stay with them for a while, however Nagisa is not convinced that she is really his sister because she is so sloppy and unlike Kotaro. It also bothers her that the two often go off to talk in secret.