South Korea is a convenient ally to have for the US Navy as they are positioned closest to throw stuff at Beijing, or to interdict the PLAN in the Yellow, and Bohai Sea. The US have docked an Ohio-class submarine at South Korea in the middle of this year. While it is not a good idea militarily, it was definitely done as a threat to China. Nevertheless, I believe that USN wants the SK navy and airforce to fully commit to becoming their asset. They will be the closest offensive force to face the PLA if SK joins the US-led war against China. To the American war planners, it is better to sacrifice the Koreans first, and then the Japanese, before any harm comes to the Americans. Hopefully by the time the Koreans and Japanese are exhausted, the Chinese would have been weakened enough for the Americans to finish them off. Not that it'll work, but I am quite sure that that is how the US would plan out their war with China.
I had considered the election of president Yoon to be the official confirmation of South Korea's entry into the US-led the anti-China alliance. Even during the previous administrations, there has been a growing trend of demonizing China more than North Korea. Ever since that THAAD deployment spat, China-SK relations have been declining. Today, regardless of how much South Koreans still hate NK and Japan, they hate China more. Couple this with the recent growing hate on Russia, with South Koreans volunteering to fight in Ukraine against Russia. This is definitely of American design. It is also my personal opinion that if SK could have its way with China and NK, they would commit atrocities that could rival that of the IJA of WWII, because of the inherent identity crisis of South Koreans to prove their racial superiority. Why? Because the SK military have committed atrocities in the Korean War and the Vietnam War.
There might come a time where ultranationalist South Koreans start to demand war on China. But North Korea will always return to the agenda. Because whether or not NK joins China to fight against SK and its allies, there is always that uncertainty about NK's position. If NK sits out of a war where China is attacked, and China is weakened, NK is certainly next on the list to be attacked. Or if China is somehow OK with NK sitting out of the war, and then beats the living crap out of SK, then NK becomes a strategic threat to a weakened SK. NK will always be a target of attack by the imperial alliance regardless if it joins or sits out the war.
For the Chinese military top brass, I do think and hope that they have calculated South Korea among the enemies that will join the US to fight China. No matter how silly that sounds, South Korea is too strategically located, and too fanatically attached to the US to be ignored as a direct military threat to China. While the SK military is not nearly as powerful as the PLA, they should never be underestimated, because they are at China's doorstep. China have to assume that the South Koreans are gonna be better-trained, and better-motivated to fight China than the Japanese or Taiwanese traitors. Because they lack the historical baggage of losing a war and getting pacified, like Japan, and to a certain extent, the ROC. SK would be feeling that it has a point to prove in East Asia that it is a top dog there. And this kind of thing would have fascistic tendencies. This kind of enemy should never be taken lightly.