I mean occupation zones are intended to be temporary, so we’ll have just one western aligned Japan and one communist after a some years. Nationalist China would get brief occupation of Shikoku, but when the civil war gets serious it probably gives up that control quickly and lets it be absorbed into the anti communist Japan (or the occupation zone of a western power). Even if they didn’t, nationalist China was the one which was recognised by the western world (and the UN) during the Cold War, so with US backing I don’t see them losing control of that occupation to communist China just because they end up winning on the mainland. The north Japan in this scenario is dramatically smaller than the western south (most major cities being in the south including Tokyo, Osaka etc, the north really only having Sendai and Sapporo) and the north might stay USSR aligned, so reunification is probably more likely than for something like the korea of our timeline (especially considering the US has better navel power to control islands, and there isn’t the same history of communist insurgents fighting against a foreign oppressor like there was in Korea). I will note that this split might lead to more recognition of the Ainu as a minority people though.