After a series of marital arguments, the wife suddenly runs out of the house. Helpless and distraught, Junshi is visited by his wife's older sister, Rin, who checks on the situation and kindly offers him advice. Grateful for her support and the secret tips she gives him to improve his marriage, Junshi promises to properly thank her. However, having rashly agreed, he ends up repaying her with his body that very night...