It's hard to predict. Historically China hasn't projected power beyond their immediate vicinity (Central Asia, Southeast Asia, Korea, Siberia) and most of the time in SEA it's been soft power rather than hard power. Maybe the US will concoct something that violates a Chinese red line and tie them up in some costly war like they are doing to Russia right now.
North Korea wants their sanctions gone so they might try nuclear blackmail. In that case Japan & Korea would probably want to do nuclear sharing with the US or have their own arsenal for retaliation.