I don't play on Savage Skies and I am pretty unlikely to play on Savage Skies in the near term simply because I am absolutely terrible at playing multiple characters at the same time.
However as an outside observer whos only familiarity with the game is the wiki. I really get the distinct feeling that neither @marsmrsmars nor @juneko are coming at this issue from a genuine concern of playing this game.
The premise of Savage Skies is that a group of ex-military people and civilians join the Sky Guard to fight fascists together. It should go without saying that members of an anti-fascist militia are not going to be fascists. The game also clarifies that you're not allowed to play ex-nazis and in light of this debate they added the additional clarification that all characters from authoritarian states need to be explicitly opposed to excesses, war crimes and atrocities.
As such I think it's very clear that the way this game is intended to be played is that no member of the Sky Guard is meant to be assumed to be associated with any kind of war time atrocity regardless if whatever military branch they are associated with performed those atrocities in the actual WW2. Not only are those atrocities by and large scrubbed out of this timeline but you should assume those Sky Guard characters are opposed to them happening and would presumably have found some way to avoid participating.
While it's fine to raise questions regarding how Hirohito should appropriately be handled, the game appears to be clearly set in the European theater and anything happening in Asia is only background. A background where even though the game is started in 1938, the 1937 invasion of China isn't on the timeline yet so assuming that a fellow member of the Sky Guard participated in the Nanjin Massacre comes across as somewhat ludicrous as you have no reason to think that event has even happened.
If your interpretation of someone having an RP hook about being a monarchist or communist is that they're a fascist complicit in war crimes, I don't think this kind of game is suitable for you. I honestly don't think there's anything the game staff can do that will make you happy because the game relies upon you taking the point of view that everyone in the Sky Guard are on the same side and you are actively looking for reasons to think they're not.