Mother Saaki harbors a secret affection for her son, Hiroki, while lost in masturbation. Hiroki, meanwhile, carries a forbidden emotion for his mother, spending his days in turmoil. Unable to confide in each other, their relationship takes a dramatic turn after receiving a letter. Discovering the truth about being switched at birth, Hiroki becomes distraught, but Saaki gently holds him, comforting him. Embracing their long-suppressed feelings, the two replace their mother-son bond with insemination sex, deeply connecting with each other.