Ripe Young Wife: The Swapping (1990)

Nozawa, a detective, had an unusually strong sexual desire, but because of his job, he could not hang out with ordinary women, so he persuaded his wife to go to a swapping club. What he was waiting for there was a couple who happened to live in the same apartment building… The two couples who have switched partners become entangled while being watched, becoming male and female.