@Kazuraki - Wow, umm in the way you put it, I'm gonna go with "No". We can all see this story is not depicting a realistic portrayal of how things would go down. But your view of how things would go down isn't true either. Does Japanese politics lean conservative? Yes. Are their common values is arguably conservative? Yes. Do they have people who continue to deny the atrocities they committed? Yes.
Is it to a point where their behaviors and inclinations are only held back by NGO, the UN, and the Western Governments? That if unchained from such influences means they would do "Nanjing x100"? No, I cannot agree with your worldview at all. I am a follower of realpolitik and I do believe that without counterbalancing power then Japan would start abuse its power (though that ignore Japan would probably be in too much chaos to exercise its straights by this point). An unrestrained Japan would behave much more ruthlessly and selfishly if such power. But to expect "Nanjing x100" is excessive.
I also have to take issue in your implied ethical valuation. Lines like "acting timid and nice because they didn't want to anger the west again" or "US troops could botch any plan" implying the west operates more on ethical principles meanwhile Japan would have those forces too (and I mean beyond the "people). Japan isn't 1920's Japan anymore. And it's not a fair assumption that Japan would go back to that state if allowed - at least no more than any other modern nation.