What happen in episode 13.5? After the last episode (ep 13),


   Everyone graduate except Otonashi and all the NPC disappear, but there's episode 13.5 where Otonashi become student council president replacing Kanade place, and all NPC and one regular student (non-NPC) appear again. Did they reset the after life world?


What exactly happen here?
The so-called "episode 13.5," titled "Another Epilogue" was released as an extra on the BD/DVD exclusive. Depicted is an short alternate ending where Otonashi remains in the school and becomes the new student council president, in order to help other students (like how Tenshi did) to pass on. It's really a "what-if" scenario rather than an actual epilogue.