The older sister, Yui, is caring and does the housework, while the younger sister, Karin, is quiet and easily influenced. The two of them live comfortably with their stepfather, who is their mother's new husband and a wealthy man. However, while their mother is hospitalized due to a chronic illness, nightmares occur... The stepfather's attitude, which had been so kind, suddenly changes, and he approaches the sisters, revealing his lust. The easily influenced younger sister skillfully leads her to sex. The strong-willed older sister forcibly impregnates him. He takes advantage of the difference in their personalities and manipulates her, controlling both her mind and body. Before they know it, the two have become female slaves competing for sexual service. "Our only value is to become stepfather's breeding bag, I'll be first, first...!" They are so brainwashed that the only thing they can think of is that...