Build Limbs

Summary

Fed up with the indecision and having to keep Kouichi out of the loop, fellow student Ikuo Takabayashi prepares to spill the beans to Kouichi but suffers from a fatal heart attack he can explain Class 3's situation. The following day, everyone in Kouichi's class begins to pretend that Kouichi doesn't exist and completely ignores him, similar to the story 26 years about the student who allegedly died but was still seen everyday by a classmate. Distraught and confused about what is happening to him, Kouichi seeks out Mei, who also suffered a similar fate at the hands of the class, and she reveals the truth to him:

There is always an extra student, an unidentifiable dead person nonetheless, in the class. Changing rosters or class assignments fails to solve the issue and eventually, the dead student brings enough bad energy into the classroom resulting in a student and one of their family members dying every month. After years of trying to find a way to prevent the constant death, the students and teachers decided to simply ignore one student and act as if they don't exist, which figuratively puts the class count back at a normal level, and prevents people from dying.