One day, Kabejiri Yuki, a high school student, looks at his smartphone and notices a strange app installed. Intrigued despite his suspicions, Yuki starts the app. Late at night, after initiating the app, a wall buttocks suddenly appears in Yuki’s room, just as described in the app’s instructions. Confused by what he sees, Yuki succumbs to temptation and engages in the act. While the app’s description contains some unsettling information, one wonders what lies ahead for Yuki.