The shadow in the classroom
From Shousetsu Bang*Bang Wiki
The shadow in the classroom is a story written by Hyakunichisou 13. It ran in Issue 57 at http://s2b2.livejournal.com/, and will be mirrored at http://www.shousetsubangbang.com/mirror/.
Other stories featuring the same characters are:
Everyone goes through the door (http://s2b2.livejournal.com/294425.html; mirrored at http://www.shousetsubangbang.com/mirror/everyone-goes-through-the-door/).