Left sexually frustrated due to her husband's long-term work assignment away from home, mother Aiko falls into a habit of masturbating to cope with loneliness. Her son Masato, catching sight of her in the act, can't suppress his intense arousal and moves closer, passionately caressing her. Initially resisting, Aiko gradually succumbs to the pleasure she hasn't felt in ages, climaxing with powerful squirting. Immediately after, Masato thrusts his rock-hard erect cock in front of Aiko, signaling the beginning of a new, forbidden relationship.