Boku to Kanojo no Midara na Utage

Tatsuya, a college student, is in love with his classmate Saki. However, he harbors a secret fetish for cuckolding, which Saki accidentally discovers.

Instead of rejecting him, Saki proposes a bold arrangement. "Are you interested, Takkun? I'm having sex with other people." With those words, the two begin swapping partners with a close senior couple, Marina and Masao. As their secret relationship deepens, other men and women join their circle, turning their private encounters into an increasingly lewd and exciting party.