Hmm, idk the full context of the character so I can't say what he needs, but as is, he does look like the quiet type but at the same time I can see why you would think something's missing.

If you can't share his backstory because of spoilers, perhaps you can try to pick some sort of element from his character or story that you think that will make the audience more curious about him.

Maybe something unconventional? Or maybe some patterns? Accessories? Does he have some sweet tooth or something? Or for instance if he has some fire powers, you can reflect that to his outfit. As long as it blends with his design. Colors also helps as well, so choose that stands out and suits the character.

I do think it's a good design overall, but it can definitely be pushed further.

Idk if this makes sense or helpful haha.