You are very silly to saying that China have zero chance against USA and Japan? If this is your assertion over this tiny rock, then Taiwan would have been a much bigger tasks for return!
What making you thinks, that Japan is so superior that the Chinese have zero chance at all? You must remember, Taiwan also claim this tiny rock island!
Also, what is stoping China from firing off missiles into that area using it as target practise sites?
You believes that America is going to risk their largest T-Bills purchaser over a tiny rock? Get real and learn a big of how real world operates.