Another possibility for a Fascist China could be the Beiyang Government surviving and drifting rightward. I think the seeds for Communist Japan could be planted during the Great Depression. Just have the USSR meddle in Japanese Affairs to have the military embrace Communism rather than Fascism.
The Second Sino-Japanese War would be strange in ATL. If the USSR did meddle in Japanese Affairs and turn Japan Communist, then it could set the stage for a Soviet-Japanese Alliance, despite Soviet desire for revenge for the Russo-Japanese War. The USSR and Japan probably invade Fascist China at the same time, with the Soviets slicing off Manchuria and Xinjiang for themselves, whereas Japan eyes South China. If there is still a Pacific War, then perhaps the Soviets intercede diplomatically to keep Communist Japan as a buffer against the Anglo-Americans. Of course this would all butterfly Japan joining the Axis to begin with (China joins instead) and the need to attack the Allies.