If the German foreign office was smart they'd try to use this to drive a nail between the Japanese and the rest of the Entente.
Of course, we know it wasn't smart.
I'm not sold on this not being able to fully tear Japan away from the Entente. Even by the 21 Demands of OTL both the US and UK were furious. If Japan indeed uses the opportunity of Europe being busy in Europe to invade China, everybody - especially the US - would be extremely angry. Not sure if this would lead to a war between Japan and the US, but there definitely will be a diplomatic crisis.What if China flat out refused the 21 demands Japan issued them in 1915 and the situation escalated to war?
Japan an early ally of the Entente - Japans Entente-partner UK as well as the US furios about the 21 demands - nevertheless war between China and Japan - - - China later still (?) joining the Entente with declaring war against Germany in hope to get support against the japanese (as China didi IOTL). -What if China flat out refused the 21 demands Japan issued them in 1915 and the situation escalated to war?