Kaiman Hitomi: Nandemo irasshai(1991)

A couple who lived an ordinary married life. In order to revitalize his slightly stagnant sex life, a husband decides to take erotic photos of his wife and post them in the wife's boast section of a swinger magazine. The wife gets excited just by taking pictures, and they have intensely erotic sex, which makes her husband very satisfied. When it was published in a magazine, the couple was very excited. Then, a reader couple finally invites them to go swapping. The couple, already intrigued, decided to participate and had an experience they had never experienced before. This stimulation may have awakened the wife's previously dormant lewdness, and she begins to seek stronger stimulation, but her husband, on the other hand, is withdrawn by this change in his wife and tells him to stop...