Shima Izumi no suwappingu (hi) sekkusu kōza (1981)

A sexually mature wife was overwhelmed by her desires. The person she chose to swap with was a lesbian friend from her high school days. She was impatient to wait for her husband, and began playing while remembering the past. Mixing in the pleasure techniques she had experienced since graduating, the lesbian play in all sorts of ways was exciting, and the two of them ascended to heaven at the same time...