Stand Up!!!! (KUMAGAI Kyoko)

From Nagareboshi Manga:

The protagonists, Hinako, Makoto, Yoshi and Yuki, are standing up!!

One day, the four are called to the principal's office and shown some scary graffiti that had been put up on the school wall. One reads, "I'll kill Shinozuka Makoto". It's their job to find out who did this, and who's after Makoto. Near-death experiences and mystery await!