Thirteen years ago, when Shiho became a stepmother, her husband's son from his previous marriage, Toshimitsu, was only eight years old. Since her husband worked overseas and returned home only a few times a year, Shiho spent nearly every day alone with Toshimitsu. One night, after celebrating Toshimitsu's success in passing his university entrance exams with a family dinner, an intoxicated Toshimitsu went to Shiho's bedroom and attempted to make his first move, but struggled. Responding gently to the situation, Shiho guided Toshimitsu's penis into her vagina herself. In that moment, a new relationship began between the two.