Monochrome Factor

The story revolves around high school student Akira Nikaido, a typical slacker living a normal life. That is, until he meets the mysterious Shirogane, a man who suddenly appears and tells him to meet him at the school that night. Though he is skeptical, he goes anyway, and subsequently gets attacked by a shadow monster. Shirogane convinces him that the balance between the human world and the shadow world has been distorted, and that Akira must become a "shin", which is a creature of the shadow world, in order to help restore the balance.

Super sadly this is the only one of its kind