Some people are a bit confused about the thing with Nene so let me explain: according to Kizaki-sensei, when a student dies due supernatural reasons, a dead person replaces them as to not raise suspicions and keep the number of current alumni the same.
Now this chapter implies that Nene died sometime in the 90s and has replaced another person at the beginning of the course; what's the reason of Chigarashi's tears then, if that means Nene just revived? Because according to Kizaki's theory, this phenomenon only works with in the campus to keep appearances so once they graduate, Nene is going to die again.