From MangaHelpers:

This is the manga adaptation of part five of the Kyougokudou novel series. As such, it will feature an investigation by Chuuzenji Akihiko and other recurring characters, though they play a relatively small role in the first volume.

The story begins with a supernatural murder mystery in an all-girls school. Sayako and Miyuki both attend a high class private religious all-girls school, and one of the bonds of their friendship is that neither of them come from a prestigious family. One day, Sayako confides to Miyuki that the teacher Honda-sensei is sexually abusing her. When Sayako hears a school legend that involves asking a demon to curse someone to die, she and Miyuki investigate the possibility.

Miyuki, an atheist, doesn't really believe in the idea of curses, even though she has a schoolmate, Yuko, who has supposedly used this method to have someone killed. Nevertheless, she supports Sayako in carrying out the ritual, in the hopes that it will give her some peace. However, after they speak with Yuko, they must face the fact that the curse may be dangerously real, and may carry with it horrific consequences. Miyuki's world is quickly spiraling into a nightmare! [tethysdust]