In 1998, Kouichi Sakakibara transfers to Yomiyama North Middle School, where he joins Class 3-3. Upon arrival, he notices an eerie atmosphere surrounding the class, particularly directed toward a quiet, mysterious girl named Mei Misaki, who wears an eyepatch and is seemingly ignored by everyone. Despite warnings from classmates and teachers to avoid interacting with her, Kouichi befriends Mei, intrigued by her enigmatic presence. As their friendship develops, Kouichi begins to uncover the dark secrets tied to Class 3-3.

The class is haunted by a curse stemming from a tragic incident in 1972, when a popular student named Misaki died unexpectedly. Devastated by the loss, the class collectively pretended Misaki was still alive, creating a delusion that led to strange occurrences. Since then, Class 3-3 has been plagued by a phenomenon where an "extra" student, who is already dead, is unknowingly included in the class roster each year. This presence triggers a series of gruesome deaths among students and their families, escalating in frequency and severity as the year progresses.

Kouichi and Mei work together to investigate the curse, uncovering its origins and the rules governing it. They learn that the curse can be mitigated by identifying and isolating the "extra" student, but this process is fraught with danger and moral ambiguity. As the death toll rises, paranoia and mistrust spread among the students, leading to desperate and tragic decisions. The narrative builds tension through a series of shocking and unpredictable events, culminating in a climactic revelation about the true nature of the curse and the identity of the "extra" student.

The story explores themes of grief, guilt, and the consequences of collective denial, set against a backdrop of supernatural horror. Kouichi and Mei serve as central figures in unraveling the mystery, with Kouichi’s outsider perspective and Mei’s connection to the curse driving the narrative forward. The series maintains a suspenseful tone, blending psychological horror with visceral imagery, and keeps viewers engaged through its intricate plot and well-paced revelations.