What Even is Despair?

[SYOC CLOSED] "All I can remember is a playback of two girls...both speaking of two different despairs." A crew of amnesiac high schoolers trapped in a desolate city with only one way out: kill their classmates. And on top of that, a traitor and a demon lurk in the shadows. How are 16 new students supposed to survive, when they can't even fathom despair itself?