Kokoro is madly in love with her older brother Takumi—despite him already dating his childhood friend, the kind and beautiful Tomoka. The couple desires a happy life together, but Kokoro has other intentions. Using a hidden camera, she records the couple's intimate moments and threatens Takumi that she will expose them, manipulating him into having sex with her. In a desperate attempt to avoid his little sister, Takumi leaves his parents' house and moves to another apartment with Tomoka. Unfortunately, Kokoro will not let go of her beloved brother that easily. [Written by MAL Rewrite]