映画版 ふたりエッチ セカンド・キッス (2011)

Upon marriage a wife and husband were virgins. They steadily improve their sexual skills day after day. After six months of marriage they are having sex every night. The wife, however, feels things are becoming stale given her husband's lack of new maneuvers in bed. One day the sister-in-law comes to meet her brother's wife and she is having relationship problems with her boyfriend. The sister-in-law insists that the man will get bored if a woman is always available for sex prompting the wife to restrain herself for three weeks.