this morning, I discovered that this kid in Godzilla Against Mechagodzilla is meant to be the kid from Hamtaro
so while GxM doesn't exist in any prior Godzilla timeline, it does exist in the Hamtaro universe, which to me implies that the sentient hamsters are some form of mutation as well, possibly irradiated by-
"Didn't take long for them to try and weaponize his blood. Warships, tanks, planes and all designed to deploy the bio weapon. We warned them of Godzilla's insane regenerative nature. They didn't listen. They should've listened" Black Mass Mecha-Godzilla
Revelation that the key to understanding Godzilla is that you must understand it is wrestling. It is wrestling. The good guy monsters like Godzilla, Anguirus, and Rodan are the Faces who you always root for because they’re YOUR GUYS. The bad guy monsters like Ghidorah and Gigan are the Heels who act like assholes and yell things like “it doesn’t matter what you think!”. The good humans like Miki and Serizawa and the Shobijin are the Jim Ross-style announcers and interviewers who comment on the match or chat with the wrestlers between fights. The bad humans and evil aliens are the corporate guys like Vince McMahon, and the giant robots like MechaGodzilla are what happens when they decide to get in the ring themselves. Rival kaiju/toku series like Gamera or Ultraman are rival wrestling companies and underground circuits. Baby Godzilla is Hornswoggle.