Japan lost everything in WWII, now they're going to lose a lot more.

7856687
Considering Japan is occupied during this time period, America will have to do the fighting and losing. They weren't exactly churning out the atomic bomb, don't forget. So that's out.

We now have a full design and it looks kickass.

7856971
Doesn’t he looks slightly similar to the shin Godzilla?

7857017
Not really.

Because,

1. Shin looks like this.
Also, if anything, ShinGoji is clearly meant to be a modification of ShodaiGoji. MinusGoji looks more like the Heisei Godzilla with some MonsterVerse elements.

2. Shin Godzilla is black with red streaks. This Godzilla sports more of a mottled brown and gray coloration with some keloid scars here and there (specifically on his ankles, his chest, and his left eye which has earned him my nickname of ZukoGoji).

3. MinusGoji's tail does not take up 90% of his body and it looks like his arms are actually fully functional, not to mention his eyes look more expressive.