Your challenge, with a post-1939 PoD, is to come up with a scenario where, by 1950, the OTL post-WWII fates of Germany and Japan are reversed.
Japan is divided into a Soviet-ruled Communist North (Hokkaido and northern Honshu) and a democratic South (rest of Honshu, Shikoku, and Kyushu), aligned to the Western bloc, with a Tokyo divided into Western and Soviet sectors. I don't see a feasible chance of Japan suffering the loss of a ethnically-cleansed sizable chunk of its national territory like OTL Germany suffered, so it is not a precondition of the scenario.
On the contrary Germany is united under a democratic government and a member of the Western bloc, and it has post-Anschluss borders minus East Prussia (lost to Poland).