Identity. Devil May Cry.

Dante thought he was the only demon hunter, he thought he was the only one able to kill demons in the entire city. One night outside his shop he hears a guy taunting someone, which is a demon. It was a Hell Sloth. Dante was about to save the guy before he got himself killed but the boy was able to kill the demon with only a switch blade. Impressed, Dante offers him a job at Devil May Cry where he happily accepts. He acts oddly though. He keeps the sides of his head shaved and refuses to let his hair get long, he always wears the same punk clothes and always wears a replica of Kaneki's mask and never takes it off. Dante thinks something is wrong with this guy and he plans to figure out what it is.