Sora, a girl with penis, is secretly in love with Aya. One day on the train, Sora presses herself against Aya's buttocks and accidentally ejaculates inside her underwear. This unexpected moment sparks the beginning of their relationship. Aya had sensed Sora's feelings and responds with a mischievous smile, seducing her. That day, they have sex for the first time—but what follows is a surprising twist…