Boku-kun returns home for the summer after living in his school dorms, only to be greeted by his two lewd older sisters, Ayami and Megumi. The bold Megumi quickly seduces the virgin youth, leading to an intense encounter where he loses his innocence. Not to be left out, Ayami soon claims him as well, leaving Boku-kun overwhelmed by the competitive and erotic advances of his sisters.
During his summer break, the protagonist finds himself caught between the desires of his two older sisters, Megumi and Ayami. After an intimate morning with Megumi, Ayami's jealousy leads her to seek her own turn, resulting in a passionate encounter for all three. Bound by their mutual lust and affection, the sisters vow to satisfy their brother's every need, ensuring he never has to look elsewhere for pleasure.