Character: Belthazar
Is your character especially logical or creative (or a complete lunatic)? Belthazar likes to think he is logical, and he is very, very smart, but he's ruled by his emotions above all and he also really likes to cook fancy stuff, so that makes him an artist of sorts.
Does your character have any echoes that Katie can see/interact with? Belthazar has a tendency to become unhealthily attached to people. His biggest one is his older sister, Caspa, who is... well, she's dead, but he doesn't want to acknowledge that. He's occasionally tormented by nightmares about her death during the genocidal purge of his home. She looks about the same age that he is now but a little taller, with long dark curls and glowing blue eyes. Definitely related.

Other things of note: Belthazar can sense mana and see the threads of magic that make things up, though I'm not sure Changeling magic is anywhere close to the magic he's adept with. If she has anything like mana, he'll be able to sense that and possibly feed off her energy (with permission, of course).