Hmm... A Natsu-like character huh?

Well right off the bat I would have to agree to Kurtmuran's two suggestions at the very least, albeit there might be some need to alter them.

I was complimented that my own homebrew was Natsu-like but I wouldn't suggest using it since its still very much a WIP and imho not as close as the two above. But your more then welcome to take at least a look if your interested, its in my sig.

Maybe you could also 'remake' a feat in Complete Adventurer [if memory serves] that allows certain class features between two classes [ex: Sorcerer/Monk] to continue growing as you gain levels between the two classes? Except maybe you could change it so that instead of the Sorcerer/Monk it be a feat for Dragonfire Adept?

Barring Homebrew, I know that Monks have a class variant in Dragon Magic that lets them punch using a single element they choose at level 1 that I believe scales [away from book so forgive me for not getting into greater detail]. Everything else I can think of has already been mentioned.

Good luck with your endeavors!