Doesn't seem like much activity here on this forum in recent times but I wanted to put this across:
I play on Xbox Live with Natsu and the vast majority of my opponents are struggling to react to 4A+B. Now, the usual thing to do here is POR 8B+G, which always works, however I feel guilty doing it. I get called a "bomb spammer", but I think it's their fault for not having the ability to deal with bombs correctly (blocking low for 4A+B, not teching when down, jumping them etc.).
Anyway, I was wondering, when you fight people who constantly get launched from 4A+B, do you unrelentingly POR 8B+G? I find myself pressing K out of PO (which does give a little bit of damage) or even B+K (nothing at all) just to satisfy their whining of air grapples. Oh, and PO B+K is a wonderful move; almost always gets you some low-hit damage in the beginning, and you can go for PO B or HOV B against a conditioned opponent blocking low.
Another thing, 2A+B, followed by the 41236B unblockable works 80% of the time for me, resulting in massive damage. I'd recommend it to any Natsu player who is unsure of how to get quick, easy damage.
Finally, I wanted to recommend the Natsu SoulCast featuring kAb to all here, it's helped me a great deal.