A6M5 was unproteced. A6M5b added the armored windscreen and possibly a fire extinguisher. A6M7 I think added more.
Ki-43 followed a similar pattern, but I seem to recal fuel protection in the Ki-43-II. The Ki-43's structure was much lighter built than the A6M's and it was known to break up when hit by a decent .50 cal burst.
The G4M1 and G4M2 were wholly unprotected. The G4M3 was fully protected, but almost none were built and none saw action before the war ended.