When the girl's parents left on a business trip, her brother invited a friend for a sleepover without warning his sister. In a half-asleep state, the girl wakes up in the night with the urge to go to the bathroom and staggers and bumps into someone's body. Finding herself in front of her brother's friend named Shidou, she nearly falls over, fearfully gazing into his face. They rarely see each other, and their relationship is strained - resentment is present, especially from the girl who finds him strange. Her brother, meanwhile, is sleeping peacefully on the second floor.