Umbral Blade

A loyal exorcist to the church, who had done many things and was well respected and revered among the church and the supernatural factions. But time, man's worst enemy second only to man itself, caught up to him, and soon he became bedridden. His son tended to him day and night, until a man called Valper Galilei, one of the exorcist's old friends, comes to him, seemingly to comfort his old friend.

But he slips in a secret concoction into the medicines that was keeping the priest alive. That concoction was a liquid form of one of the Excalibur shards, Umbra. The concoction turns him to a monsters and Valper makes him kill his son. But his rage against Valper soon breaks him free, and he brutally maims the old Priest, before fleeing, never to be seen again