Akai hatsujô: Mashô no kaori(2014)

Moe moves in with her junior colleague Kaori to help her out after she's been stalked. The original cause of the stalking was Kaori's obsession with men, but from the very first night they started living together, she repeatedly has passionate sex with men. Moe, who is plain and inconspicuous, is bitter about Kaori's behavior.