Mizuhara Sana, a widow who lost her husband early and raised two sons alone. Her eldest son, Koichi, is mature and healthy, while her younger son, Yuki, is childish and still emotionally dependent, lacking sexual knowledge. When Sana begins teaching Yuki about sex through handjob and blowjob, Koichi finds out and starts craving her body too. A rivalry begins between the brothers over their mother, and to prevent conflict, Sana proposes an incestuous mother-sons threesome. A complex and shocking story unfolds, entwining the boys' desires with their mother's compassion.