A story about two siblings who became step-siblings after their parents remarried. The younger sister (voice) develops an unhealthy obsession with her older brother, leading them to secretly form a relationship behind their parent's back. While studying, she receives oral pleasure from him, and in return, performs passionate blowjobs on him. Their first time together occurs when they are left alone during a trip by their parents. They share intimate moments in the bath, expressing how happy they are that it was each other's first time. The younger sister is extremely sensitive and easily climaxes due to her high level of arousal. One day, jealousy drives her to forcefully have intercourse with her brother while his classmates watch, claiming that he can only satisfy her. As he leaves for college, they promise to make the most of their remaining time together before embarking on a long-distance relationship. Despite this, the younger sister continues to fantasize about him and masturbates thinking about all the pleasures they shared.