When Iroha got married ten years ago, Iroha became her husband's wife and the mother of a junior high school student son. Her husband had a son from a previous marriage, and she was worried about whether they would get along well, but they lived happily. However, she had not had sex with her husband for years and was frustrated. One day, her husband bought a balance ball. She invited her son to exercise with her on the balance ball, and her son became excited. Her son started rubbing Iroha's buttocks. Iroha resisted and tried to run away, but her son pushed her down...