So much so that thousands of Koreans took advantage of the chaos after World War II to smuggle themselves into Japan. It was then the Koreans who claimed systematic discrimination and insisted on setting up a separate Korean school system in Japan.
Even today, about one third of ethnic Koreans in Japan claim sympathies with the north and then whine about systematic discrimination because the Japanese authorities keep an eye on them. Some even claim it is the Japanese who exclude them from the Japanese public school system.
Most of the remaining two-thirds have integrated fairly well into Japanese society, though many still opt to send their kids to Korean schools to preserve their language and culture.
There is no law preventing any legal foreign residents from sending their kids to Japanese public schools. Our own children all attended. They have an interesting system of pairing kids with someone whom they think they can help each other. My own daughter (who was born and raised in Japan) had some interesting pairings including a girl who had been born and raised in Texas, where her father had been posted and recently transferred back to Japan. They became good friends as my girl helped the Japanese girl with her Japanese and the Japanese girl taught my daughter to speak English with a Texas accent.
Koreans, Chinese, even Russians and all the rest of Far East community won’t give a flying huck on what Japan has become under American occupation. Japanese are fanatical racist bloody monsters for them forever. It is a kind of archetype in that part of the world. Nobody likes Japanese. Japanese reflecting this crap and don’t like themselves too.