History of Koreans in Japan has a complicated story. But basically ethnic Koreans are treated as a second class citizen in Japan.
A Korean-American friend told me this story. He worked with a Britain/Ireland born coworker who was working in US at the time. Blond, European. He traveled fair bit to Japan. He knew this guy was Korean-American and in a conversation he asked the Korean-American why Japanese didn't like Koreans.
The EU guy said when he visited Japan in 2000, Japanese told him they didn't like Koreans.
And than in 2005 or so, he heard from Japanese that they liked Koreans.
In what context the Japanese told a blond European guy why they liked or didn't like Koreans is unknown.
This EU born coworker was confused what changed in that 5 year period.