大学生活を送る上京先から数年ぶりにお盆帰省した奏太は地元の何も変わらない景色に心地よさを感じながら3年ぶりに実家に帰省したー。しかし実家に帰って出会ったのは、●校のクラスTシャツを着て、ゴミ部屋の部屋に住むアラサーの姉・クレアだった。奏太が上京している間に離婚した彼女は、毎日BLを観てダラダラ過ごす喪女と化してしまっていた。そんなある日、ふと姉の部屋を覗くと汗をかきながらとんでもないデカ尻をさらけ出しオナニーをしているのを目撃してしまう。姉の変態オナニーに目が離せなくなっていると、姉に見つかり、部屋に無理やり引きずりこまれて…。

Returning home for the Obon holiday after several years away in Tokyo for university, Souta felt a sense of comfort at the unchanging scenery of his hometown, his first visit in three years. However, the person he encountered upon returning home was his older sister, Claire, a woman in her late twenties, wearing her high school class T-shirt and living in a messy room. Having divorced while Souta was in Tokyo, she had become a lonely, unattractive woman who spent her days watching BL (Boys' Love) movies. One day, he happened to peek into his sister's room and witnessed her masturbating, sweating profusely and exposing her enormous buttocks. Unable to take his eyes off his sister's perverse masturbation, he was discovered by her and forcibly dragged into her room…