In the interwar period, Germany became close to China, and trained their troops which became useful for their war against Japan. Hitler ditched friendship with China in favor of Japan, but still Germany did help a bit.
What if Germany saw a potential ally in China before WWI and gave the Chinese economic aid and military training in exchange for raw materials and a defense alliance formed? China has a gigantic border with Russia it can cross, since their's no separate Mongolian country yet, and it also borders British India and French Vietnam. Could a well trained Chinese military change the course of events?
Since Japan is in the Entente, I guess they can legitimately take Manchuria now if they beat China.