Well the theme of enduring Japanese Empire was never throughly discuss (maybe one of the reason cause we expect them to have them beat by the american one way or another more than the Nazi)
Well I'm pretty sure that if they lasted more than a decade they would have end up slacking off one time or another. One way they could market the Co-prosperity sphere to those living in it would be "asian empowerement" rather solely japanese one.
Could "Korea united with a Tolerant Japan" end up with Japan developping the same identity problems that Canada/Quebec have?
The theme of an enduring Japanese Empire starting around WWII is discussed, and promptly dismissed as very unlikely. However if we start further back, perhaps things can work out better.
Exactly what I was thinking. Acknowledge nationalism, take over the top level but run the place loosely assert Japanese cultural superiority because they were the only ones to industrialize and fight off the West, promote their culture as the goal to aspire to and once you're there you're a proper member of society no matter where you happen to be from. How the British did it, to some extent, in their imperialistic days.
Canada doesn't have an identity problem, nor does Quebec. We have a certain disagreement about some things that are well outside the realm of this thread. (Short version: Quebecois decline to accept reality, nobody else particularly cares.)
As for Japan-Korea I think the Japanese will go for cultural superiority (instead of just being racist, as IOTL). Will it work? I don't know, but I imagine a lot of back and forth influences.