The son-in-law and the mother-in-law in their youth

Shinichi-kun, can you abstain for a month before the trip?” This was supposed to be a hot spring trip without his family, but he took advantage of it and his wife asked him to be his mistress. However, my wife is not interested in having children and refuses no matter how many times I invite her. When I was wandering around the motel room at midnight trying to appease the desires that had accumulated during my abstinence, I happened to witness my mother-in-law's seductive bathing appearance.