Tsubaki lives with her husband and son. Even after 30 years of marriage, she continues to have sex with her beloved husband at night. However, her husband has recently become weaker, and she has difficulty reaching orgasm, so she has to pretend that she "came". Tsubaki masturbates alone, hiding it from her husband. One day, her son comes home drunk. Tsubaki tries to take care of her son, who has fallen asleep in the entranceway. Her hand reaches out to the bulge in her son's pants, which has grown larger without her realizing it, and she ends up straddling him...