Son Kousuke harbors secret feelings for his mother, Saki, while drowning in his own desires. Saki, too, though deeply loving toward her son, finds herself unable to suppress her emotions and indulges in daily masturbation. Unable to confess their true feelings, both remain trapped in restless longing. One day, a letter from Saki changes everything. Upon learning they were switched at birth, Kousuke erupts in rage—yet Saki gently embraces his pain. The suppressed emotions they've held transform into an intense maternal bond, soon deepened through creampie breeding sex, tightly binding their hearts together through primal mating.