Kôkishin no tsuyoi gibo: Hirugao no kanshû (2007)

Masayuki spies on his mother-in-law, Mayumi, as she indulges in masturbation in the restroom late at night. The next moment, he wakes up in his room, realizing it was only a dream. However, the following day, he witnesses Mayumi entangled with his girlfriend...