There's also The Royals. I haven't read it, but I know it's about European royalty having super powers, fighting in a war that's analogous to the world wars.
I agree that almost every superhero story is a kind of alternate history, more so than most fiction.
Japan is ruled by Emperor Jimmu as well, I believe.
I read Royals and summing it up:
Every king and queen and etc have superpowers. Throughout history they led their nations in wars as first line generals until the 18th century when their influence start to diminish especially when democratic revolutions happen. Sure the royals have superpowers but they can be kill like normal people. Apparently there is a gentlemen's agreement that forbid the royals from ever physically engaging in wars in order to prevent escalation.
That is until WW2 occurs when a young and idealistic English prince refused to become a bystander in the Battle of Britain and start blasting German bombers. Unfortunately this turn of events brought Japan to unleash their Royals and forcing the Allies to focus solely on Germany. Nazi Germany on the other hand had nearly zero Royals because Hitler had a very bad diatribe against the old German nobility like in the real world and had them purged.
The story ends bitterly in which Berlin is nuked and all the Royals are dead after a failed D-Day invasion. Emperor Jimmu is reining in a very cowed Tojo.
