Satomi, a shy and gentle stepmother who cares deeply for her introverted son Ryota, feels joy when he invites his friend Daisuke home one day. However, her secret is exposed when Daisuke catches her in the living room, calling out Ryota's name while masturbating. Blackmailed on the spot, Satomi is forced to submit to Daisuke's demands. Obediently following his commands, she gradually transforms into his personal sex slave and cumdump, surrendering her body completely.