Isaku Respect (2001)

Kotomi was looking forward to a fun summer vacation. Until she found the note in her bedroom. Filled with extremely personal and revealing information about her, Kotomi is forced to follow the note's instructions and go to the old school building. Once there, she discovers that she's not the only one. Many of her classmates including the headstrong Miyuki are also there. But when everyone is suddenly trapped inside the building and girls start disappearing, it's only the beginning of the nightmare.