Spoilers? Probably.
In the second series, they explain (very vaguely though) that each story arc is actually some sort of "temporal loop", where one of the characters is trying to alter the town's fate. But something goes wrong each time, and things don't just repeat themselves (the town dying, someone murdering someone else), but even the reason for all the deaths changes. One time, it's an alien virus or something; the next, it's a secret government experiment with gas weapons; another time, it's all in one of the character's mind.
The person is question is actually Rika (sp?), the youngest girl, with the purple hair. She's some sort of bridge with the local god or something. They show another young girl in a miko uniform sometimes. It's why she's always talking in two different voices and personalities.
Basically, you need someone to walk you through the maze of confusing stories and characters and whatnot.
I charge $35 a tour, and there are no refunds.
Understand?