How does that follow? Even if you end up with a larger population of ethnic Japanese, why would you get any significant influx to Korea? That peninsula would still be a substantially poorer area than metropolitan Japan, with an abundance of unskilled labour and a rising class of trained native professionals and a reputation as being home to people who are surely not Japanese. What would be the incentive for more Japanese to move there? If anything, you would be much more likely to see more net migration from Korea to Japan.These are good points, but I'd like to add one thing. With no WWII, Japan probably doesn't see the rapid economic growth it did post-war IOTL, no economic boom probably means the birthrates don't collapse nearly as soon, so Japan may very well be able to flood Korea with millions of Japanese. Obviously not becoming the majority, but becoming a very sizable group making it easier for Japan to control the peninsula. The same thing probably happens in Taiwan, only the Japanese population might overtake the Chinese population there due to its smaller size.