While her husband is away on a long-term business trip, Tsubaki lives alone and struggles with loneliness. Worried about her, her newlywed daughter and son-in-law Yasuo suggest moving in together. Though Tsubaki’s emotional loneliness begins to ease, her physical desires remain unfulfilled. One night, she accidentally catches Yasuo masturbating. Shocked by the size of his huge cock, she is left speechless—and soon decides to seduce him. Yielding to his stepmother’s aggressive erotic advances, Yasuo finds himself falling deeper and deeper into her trap.