Without anyone noticing, the total number of people in the class increases by one extra. Then, at least one person in class 3-3 dies every month... As a countermeasure, someone in the class must be treated as "non-existent". To make up for the "dead one" in class 3-3, Misaki Mei was chosen to be "non-existent" this year. Sakuragi Yukari and her mother; Mizuno Sanae; Takabayashi Ikuo. One after another, more lives continue to be claimed by the "Calamity". And now Kouichi has been chosen as the second "non-existent" student. But once the Calamity has begun, it will not stop... Who is the "dead one"?