How can you make a character instantly relatable and sympathetic?
Make him suffer for his super powers, of course!
That is, ask yourself two questions: What makes the character special? And what makes the character suffer for it?
I could wax philosophical about why we as readers enjoy characters who suffer for their super powers. Is it because we are vain? Or is there something deeper? I leave this for you to think about as an intellectual exercise.
By “super powers” I do not necessarily mean fantastical super powers. I would consider being royalty a super power, or being exceedingly talented in some way or another. A musical genius? That’s a super power. A talented ninja? That’s a super power. A famous actor? Super power. The point is that it is something the reader would want for themselves. It’s something that makes the character special in a good way. Certainly if you read and write a lot in the fantasy genre, the super powers tend to be fantastical in nature.
But if we stopped there, we’d merely have a short daydream, not a sympathetic character who can drive a story. The key ingredient to putting this special-powered character through a story is to make him suffer, and, more importantly, to link that suffering to his super power somehow. In this way, it is that very power that makes him special that also becomes the source of his problems. Using super powers always backfires on the hero, at least at the beginning of a story.
Some random examples:
Ender of Ender’s Game. He’s a genius. And he’s thus torn away from his family and forced to undergo extensive military training that pushes him to his psychological limits. He suffers for his powers.
Batman of, well, Batman. He’s insanely wealthy. But when he uses wealth to make himself into Batman, he’s forced to push away important relationships and hide his true self from the world.
Jean Valjean of Les Miserables. He’s insanely strong. But when he uses he strength to save a man trapped under cart, he blows his cover and is chased by the law. He suffers for his powers.
Really, almost every story features a hero suffering for his powers in some way, but the sooner and clearer you can introduce these elements to the audience, the more effectively you can get them into the hero’s shoes, and they’ll care about your character and his story.
At least, that’s my theory.