When we feel angry or upset with someone, we might not want to be friends or talk to them. That's how some Koreans felt with the Japanese many years ago.
Korea and Japan didn't always get along, and there were some problems between them. Some Koreans didn't like how the Japanese treated them in the past.
A long time ago, Japan took control of Korea and made it one of its colonies. This meant that the Japanese made all of the important decisions and treated Koreans like they weren't as important. Koreans had to speak Japanese and follow Japanese rules, and some people didn't like that.
Japan also did some bad things to Koreans during World War II. They made Korean people do hard work and took away their freedom. Many people were hurt or killed, and this made Koreans very angry at the Japanese.
Because of these past events, some Koreans still feel upset about what happened. They might not want to buy Japanese products or visit Japan. But it's important to remember that not everyone in Japan did bad things to Korea, and we should try to be kind to everyone, even if we don't always agree with them.