[quote=Pasta Sentient]
It's been 3 years and since then China/FFGB have been working to heal the rifts. In addition, China most likely sees the war in Europe as an opportunity to take back lands From Russia. It is opportunistic. Also since Japan is allies with China, they will join them to get a piece of the Russian pie.
[/quote]

Are we ignoring the fact that the Taiping Rebellion had just ended as well and that the people of China probably aren't exactly keen on angering a power which not only have access to far better technology than they do in a military conflict, but can very easily dispatch a relatively small force to hold them back with. Even in a hypothetical situation where the Chinese/Japanese did win, they'd have suffered so many multiple losses in the process of doing so in an already unstable nation.