Watashi, Musume no Tomodachi to Sekkusu Shiteimasu.

After the final exams, Kana stays overnight at her friend Momo's house. In the middle of the night, she wakes up needing to use the bathroom, so she slips out of bed quietly so she wouldn't wake her friend. As she approaches, she heards the sound of running water and an older woman's voice coming from the bathroom. Kana secretly peeks in and sees the Yuu, Momo's mother, masturbating. The scene arouses Kana, who begins to touch herself as well, but Yuu notices...