In the spring of 1998, 15-year-old Kouichi Sakakibara has just relocated to the town of Yomiyama, where he is scheduled to attend Yomiyama North Middle School. However, a past injury flares up, resulting in his hospitalization and causing him to miss the first week of classes. Although he recovers swiftly, he encounters Mei Misaki before discharge—a peculiar girl with an eye patch whose cryptic behavior sparks a subtle interest in him. At Yomiyama North, Kouichi is assigned to Class 3-3. Yet, beneath the seemingly innocent atmosphere, he perceives the class's behavior as strange: everyone appears tense and watchful of his actions. Furthermore, while Mei is a student in the class, neither classmates nor teachers acknowledge her, acting as if she does not exist. As further oddities emerge and questions multiply, no one is willing to provide Kouichi with answers. With few options to satisfy his growing curiosity, Kouichi begins to seek Mei's help, disregarding warnings from both the class and herself.