So before the Russo-Japanese war, Japan had been seeking to partition Northwest Asia between themselves, with Japan gaining Korea and Russia gaining Manchuria. Russia rebuffed these, Japan attacked them and eventually ended up dominating Korea and Manchuria.
But what if Russia was receptive of these approaches, and they agreed to divide Korea and Manchuria between them? And what if they became close allies afterwards? Could make the situation in East Asia interesting.
Extra points for close alliance between them in a World War 2 situation (if World War 1 happens).