I think there’s still some confusion over Godzilla’s biological sex.
Even if we take Godzilla to be male, that doesn’t mean his name can’t be first-declension. Some first-declension nouns like agricola and poeta are masculine. Many foreign names — particularly names of Greek origin — are first-declension and masculine. Examples of those include Aeneas and Andreas.
Non-Greek masculine names ending in -a and declined in Latin’s first declension are transliterated into Greek, take the termination -ς, and are declined like νεανίας (“young man”): e.g. hic Caligula, huius Caligulae becomes ὁ Καλιγούλας, τοῦ Καλιγούλου.
Some of the non-Greek names in -ας also have a Doric genitive singular in -α: e.g. ὁ Ἀννίβας (hic Hannibal), τοῦ Ἀννίβα (huius Hannibalis).
