A6M5c and on had self sealing fuel tanks. A6M5b may have had some, but I don't recall.
The Ki-67 had self sealing fuel tanks.
The Ki-44, Ki-84, H8K2 "Emily", G4M3 "Betty", B6N, B7A, ect, ect all had self sealing fuel tanks.
Only the early war Japanese aircraft are underbuilt and unprotected, and even then not all of the follow that rule. Mid-late war Japanese aircraft are very much like every other nation's.