Prologue: An interesting find

At the day like any other, Kushida KIkyo found a DVD casette, entitled "0".
Confused, she told about it to her friends in her class and, surprisingly, most of them were intrigued by the possible contents of said tape.
They persuaded her to inform everyone in their class that they'll be having a watching session after classes.
Who skips an opportunity alike that one? Obviously, there are such people, but not the girls in class D! Maybe it was a great movie? Or was it a secret message from the school? Who knows, but that's the interesting part, isn't it?

The whole idea is the characters finding DVDs across the school. Sometimes, they wouldn't be in order, so the wait would have to be prolonged