So my initial reaction was to say to just take inspiration from cosplayers who make enhanced/fancy versions of rather basic character designs, but I see that you still wanna keep it simple so we wont go that route. I'm not sure exactly what to do with him since he already has a strong "protagonist" look to him. If you lined him up with the official characters I'd honestly not be able to tell the difference. I'm not familiar at all with the games, otherwise, I'd suggest specific elements to incorporate into his look, but that is something you do know and I'm sure you'll use.
If you really wanna change his look try playing around with his shilloette a bit, he already has the distinct clothing shape down but maybe try moving the shapes around like puffy top shoulders or dropping it down into drop shaped sleeves, just little things like that. I'm looking at the game and it seems to favor the rounded shape look just cuz thsts how it's rendered, I'm betting you already have that in mind. Try drawing him just as his "shadow" so you can build a look without thinking much about all the details.
If you do wanna go the fancy cosplay route I'd check out: Raine Emery, funnily enough I think Homestuck cosplayers started the trend so thoes are good to look at, also I'm realizing I'm blanking on names now.
He already has such a strong look I'm exited to see what you do with him next