This clause should honestly be cited more
Why? It’s just become relevant again in light of Japan’s recent idiotic remarks, and it is an incredibly serious clause to invoke that you do not want to cry wolf with it to dilute its power.
The Enemy States clause doesn’t give the allies cart Blanche to use military force against former axis powers whenever they want. It does, however, give them extraordinarily deep authority to use military force far beyond the bounds of normal self defence. It’s essentially a SnapBack mechanism to revert back to WWII conditions, and allows allied states basically to do full conquest and occupation in order to eradicate fascism from the entire society of former axis powers.
What China is saying by citing these clauses is that China will view any Japanese involvement in an AR scenario as satisfying all of the conditions necessary for it to trigger the States clause. That’s about as explicit as Beijing ever will state that if Japan starts a fight during AR, the fight will absolutely not end with merely the annihilation of its expeditionary forces, and that China will do what the Americans failed to do after WWII and fully cleanse Japanese society of fascists, which basically means full invasion and occupation of the Japanese home islands in their entirety.
Simply put, this is China’s way of saying, if you really want an actual existential threat to your nation, go ahead and try me.