Gakkou Gurashi episode 3 shows how it all started. Nice ambiguity in the use of Megu-nee’s PoV. If you can handle the creeping darkness, it’s pretty much the only thing worth watching this season.

Speaking of which, apparently if you visit the official site between midnight and 4am Japan time, you get the “reality” version. (update: it’s controlled by Javascript, so it works in your local time)