Reiji Shiratori

He's a boy of Rin's age who's about to go to True Cross Academy, but since he's a bit of a delinquent in his free time he finds that he must pay Rin to keep his mouth shut about it since Rin saw him when he was about to kill some birds with a crossbow.

[Spoiler] He's later possessed by a demon named Astaroth. When he finds out that Rin's also a demon, he tries to get him so he can bring Rin to Gehenna. [/Spoiler]