Kenta, the stepson, had been secretly watching his stepmother Reiko ever since his father remarried, observing their daily close encounters. One day, he discovers that the vibrator he thought he had discarded is being used by the adults. Realizing this, he confronts Reiko, accusing her: "You used my stuff without permission." As punishment, he forces her to masturbate right in front of him. The scene unfolds into a raw, intimate portrayal of the strange bond between stepmother and stepson, entwined with forbidden temptation.