They don’t hate each other. It’s far more complicated than that and is the reason this detente might work. Koreans hate the Japanese because of WW2. The Japanese view the Koreans as slaves, worse because of the refugees from the war, they’re treated like slaves in Japan. You want to talk about human rights abuses, Japan has that on lock. So the Koreans continue to hate Japan.

Japan and Korea fear China. And rightfully so. China protects N. Korea. Which is an US enemy, so if S.Korea wants USA protection, they too have to hate N.Korea. But this means they have to fear China. Japan fears China because they did the same thing to China in WW2, and fear a Chinese reprisal, though they don’t enslave the Chinese in Japan.

So, for the detente to work. China needs to convince S.Korea that under their protection, N.Korea won’t attack. And Japan just has to fall in line and understand Korea is on equal footing with Japan. I’m not saying it’s easy, but if USA really does remove itself, then these pieces have to fall in line.