Never underestimate the deep Chinese desire to repudiate the last 300 years of history. They have already done this in many ways, but they lack a real military victory over a former victor. China did not won WW II, they hosted the war while the USA won it. Of all former enemies, Japan is the most suitable to provide a quick military victory ending without substantial losses or a nuclear exchange. China may believe they can defeat a Japanese fleet, take some islands, and then offer a choice between a settled peace or a massive SRBMS attack.
What would we do? Likely nothing. What would Japan do? They are a geriatric, stagnant country. The Chinese may be willing to toss those dice.
Stand by for an Indo-Japanese alliance. China might be left getting all of their oil from Russia. The Chinese don’t have the navy to force open those LOCs.
That may be a big mistake. Japan's culture has always been a very martial one, where death is preferable to losing face.