I think that Godzilla is Aquamans pet/ally. Why? Because Godzilla lives most of his time in the sea and Aquaman is the king of the seas. And Aquaman is also friend to all sea creatures like whales and dolphins and as we know, Japan likes to eat sea creatures. So that's why Aquaman sends Godzilla to attack Japan because they keep killing his whale and dolphin friends.

I think this was also talked about in one of the South Park episodes, but I don't remember.

You can find the original art from my deviantart page:

http://souleatersaku90.deviantart.c.....-Sea-618431494