Japan doesn't. It is essentially a US vassal state when it comes to international disputes. For China: Where would they put that money? They can't keep it in

Japan doesn't. It is essentially a US vassal state when it comes to international disputes. For China: Where would they put that money? They can't keep it in the Yuan because it strengthens their currency which destroys their export economy. So they have to buy other currencies to reduce demand for their currency while strengthening others. Which currency can they go to? The answer: USD. It's the only one that can support their scale. Sure can they make up another currency? I think they've been trying to do a BRICs currency for a while now. However, you can be sure if that gains traction that the US will start doing something about it, either covertly or kinetically. It is that much of an existential threat to the US.