OZ, a virtual realm connecting the globe, has surged in popularity. Nearly universal access allows its "citizens" to personalize avatars and partake in diverse pastimes, from shopping to socializing. With numerous user-friendly features, society has grown deeply dependent on OZ: fire departments utilize it for emergency response, physicians monitor patient vitals at will, and it is even entrusted with the safe return of the asteroid explorer Arawashi. Kenji Koiso, a mathematical prodigy and part-time OZ moderator, is invited by Natsuki Shinohara, his school’s idol, to join a summer excursion. He is unprepared for the request to pose as her fiancé at her grandmother’s 90th birthday celebration. Soon after arriving at the Shinohara family estate, Kenji receives an enigmatic coded message on his phone from an unknown sender daring him to decipher it. Leveraging his mathematical skills, Kenji cracks the 2,056-character code within a single night—unaware of the turmoil that will soon erupt...