Earlier quoted context omitted.
Historically, Korea was repeatedly invaded by Japan. More recently, Korea was a Japanese colony between 1910 and 1945, during which the Japanese ruled with an iron fist and did their best to destroy Korean identity by forcing people to take Japanese names etc. https://en.wikipedia.org/wiki/Korea_under_Japanese_rule https://en.wikipedia.org/wiki/History_of_Japan%E2%80%93Korea...
Which certainly explains why Korea doesn't like Japan, but why does Japan seem to dislike Korea so much?
See https://www.upi.com/TOP_NEWS/WORLD-NEWS/2019/04/17/ANTI-KORE...