Seventeen-year-old Kyousuke Kousaka's strained relationship with his younger sister, Kirino, takes an unexpected turn when he stumbles upon a DVD case for a magical girl anime in their household. To his surprise, the case actually hides an adult video game, sparking a chain of events. As Kyousuke delves into this discovery, he unravels a hidden world of moe anime and bishoujo games meticulously collected by his sister, leading to a newfound connection between them.