I Am The Murderer

When Rin was born Satan gave him a curse that would activate when he was five and has made Rin's life a living hell ever since. A few weeks after Rin came to True Cross Academy a murderer was the gossip of city and school. But what's really scaring the students is that the murderer is only killing the students. Who is the murderer and what does Rin's curse have to do with this and why is Mephisto so upset about his chess pieces dying I thought he planned this?

WARNING:
Cussing
Gore

DISCLAIMER:
I do NOT own Blue Exorcist/Ao No Exorcist
Cover belongs to me