Ushio

Age: ?
Hair color: Blonde
Eye color: Red
Height & Weight: (so far no one’s been able to get close enough to really tell)
Family: ?

The villain! Ushio is a half-demon of very mysterious origins. Nobody has the slightest idea where he's from, or what his motives are. He appeared out of nowhere twelve years prior to the beginning of our story, when he attempted to kill Kasashi. Her parents, both considerably strong mages, fought to stop him and died protecting their daughter. Ikue arrived on the scene in time to save Kas, and banished Ushio into a void between dimensions. He's been accidentally set free when an unstable Gate Linette was testing rerouted itself through his prison and plopped both of them face first in a Tokyo back-alley.

Ushio is, to put it bluntly, utterly fucking nuts. He's psychotic, obsessed, and driven only by an unexplained urge to kill Kasashi. He and Ikue appear to have a long-standing hatred of one another, but no one is certain exactly why that is. To be honest, nobody is certain that 'Ushio' is even his actual name; it's just what Ikue calls him, and he seems to answer to it as much as he does anything else.

Like Kasashi, Ushio is psikinetic, and has had much longer than she has to hone his power. He also has demonic regenerative capabilities, i.e., he heals really freaking fast, and won't be stopped by anything short of a mortal wound. This guy just doesn't seem to feel pain.

While he's undoubtedly dangerously insane, Ushio's also a smart sunnofabitch. He doesn't attack blindly, or without having some motivation or purpose. The combination of his power, obsession, and cunning, may turn out to be the end to our protagonists.
(Oddly enough, he has the largest fanbase of all the characters...go figure)