Eri and Kiyoshi are in their third year of marriage. Although their relationship is good, the number of times they have sex is steadily decreasing... Eri feels unsatisfied, but she can't ask Kiyoshi, who is indifferent, so she secretly consoles herself by masturbating. One day, she is seen masturbating by her brother-in-law Takeshi, who often comes over to visit. Eri desperately tries to hide it, but Takeshi assures her, "It's nothing to be ashamed of," and presses her into a relationship. Even though she knows it's wrong, Eri gives in to her Kokoro and Takeshi's aggressiveness, and gradually reveals the desires she had been hiding...