Wakazuma hitori ecchi: Yorumade matenai (2005)

Miwa, a newlywed, has been living a life of sexual frustration ever since her husband suddenly developed impotence. One day, unable to hold back any longer, she masturbates. Kuniko, the president of the apartment complex's residents' association, watches the scene unfold via a hidden camera; she had installed such cameras in every unit after her own husband had an affair with a resident. Kuniko visits Miwa, reveals the existence of the hidden camera, and declares them "masturbation buddies." Meanwhile, Miwa's husband, Junichi, is meeting up with a senior colleague named Suzuko for a part-time job...