Japan was contemplating initiating a war with China if PRC China chooses to perform any action to reunify China with ROC China. Any action that Japan considers "against its interests". This isn't bullying from either side or whatever interpretation people around the world are coming up with, this is creating a narrative of initiating war against China and going on the offensive. The matter cannot be treated lightly for Japan given the history in the last century - defeated aggressor nation that everyone including Japan agrees that Japanese history leading up to and until their surrender, was that of an aggressor, they agreed to terms of surrender which is to never create a military that enables these things to occur in future.
Okay the modern history is one where the US hegemon is increasingly in the decline and wishes to leverage Japan's capabilities against its main rival, China. Japan can be considered whatever you want - puppet, useful idiot, fascist, whatever. These thoughts need to be crushed.
If it were Japan mounting a defense against a Chinese invasion of Japanese homeland that isn't disputed, fair enough. This is Japan wanting to invade China to stop China from reunifying China... which Japan officially agrees with. Japan recognises PRC China as the rightful China. It only pays lip service to the "status quo" ROC China to keep China from reunifying, as little as that does in terms of securing China's lead over the US which isn't something that will be happening, China's lead over the US has already happened and will only be increasingly obvious to the most hardcore China haters out there. It's not going to be a good life for them if they continue deluding themselves. We got grown adults coping so hard they believe XPeng's robot is a human in a suit, then an amputee in a suit, then a robot on support cables with trick videography, now the whole thing is AI generated. However, it's kinda easy when your rival is so utterly pathetic.
How should China respond? Well it has voiced its anger, Japan won't back down because it's the banzai charge people we're talking about here. Luckily, they have barely a shred of testosterone left and if it were up to a proper hawkish China which the West always claims China to be, Japan would be facing immediate economic action backed with the threat of military action against disputed islands. Luckily for Japan, China is led by overly cautious folks and word play is all that will happen between the two sides until months later and all is usual. Nothing ever happens. China is not as irresponsible and hot headed as Russia, sometimes to its fault.
