Those are taboos in South Korea.
Hyung-Sung Kim says:
After the end of WWII, the anti-Japanese brainwashing began in South Korea. Our first president (the military dictator) Syngman Rhee massacred hundreds of thousands, if not millions, of us.
https://en.wikipedia.org/wiki/Bodo_League_massacre
In order to cover up his atrocities and maintain legitimacy, he needed a common enemy, and Japan was an easy target. So he started the anti-Japanese brainwashing in schools and in the media. And every successive president after him had to outdo his predecessor on anti-Japanism in order to maintain legitimacy.
The following book illustrates very well how our first president, Syngman Rhee, used the anti-Japanese brainwashing to cover up his massacres.
The Politics of Anti-Japanese Sentiment in Korea: Japanese-South Korean Relations Under American Occupation, 1945-1952 (Contributions to the Study of World History)
In this book the author, Sung-Hwa Cheong, concludes that Syngman Rhee deliberately stimulated anti-Japanese sentiment as part of a calculated policy that originated in his own political insecurity.
The South Koreans who were born in the 1980’s & 1990’s grew up with Japanese anime & Japanese literature (Haruki Murakami & so on) because in the late 1990’s South Korea started allowing Japanese culture to come in. (Japanese culture was banned in South Korea until then, believe it or not)
These generations typically say, “We like Japanese culture & people. If the Japanese accept our history as the right history, we can get along with them.” This means that when these generations realize that their history is not the right history but the brainwashed history, they will get along with the Japanese unconditionally.
Will they realize that their history is not the right history? I believe they will thanks to the internet & social media.
For example on internet, the South Koreans now have access to the history textbook comparison study done by Stanford University.
http://www.nippon.com/en/in-depth/a00703/
http://aparc.fsi.stanford.edu/research/divided_memories_and_reconciliation/
This study found that the Japanese history textbooks to be based on facts, the Korean history textbooks to be heavy on nationalism.
So when the generations who were born in the 1980’s & 1990’s become the movers and shakers of South Korea, (i.e. key politicians, newspaper editors, etc.) the relationship between South Korea and Japan will improve dramatically.
Right now, the South Korean society is dominated by the generations who were born in the 1950’s, 1960’s & 1970’s. These generations were raised with anti-Japanese brainwashing at schools, and they had no exposure to Japanese culture growing up. So they are hardcore anti-Japanese.
The generations who were born before 1945 (like my grandparents) are generally very sympathetic to the Japanese because they experienced the annexation period. The reason why the Korea-Japan relation has deteriorated so badly in the last 20 years is because most of them have died, and the generations born after the war came into power.
http://lang-8.com/131728/journals/214060997370493754059169827427047084412
Our presidents up to Kim Dae-jung all spoke Japanese fluently because they experienced the annexation. Park Chung-hee was anti-Japanese publicly, but in private he shared drinks with Japanese politicians speaking in Japanese. When the Japanese emperor Hirohito died in 1989, Kim Dae-jung went to the funeral and took a deep bow toward Hirohito’s coffin. This would be unthinkable with our last three presidents.
Professor Choi Ki-ho of Kaya University was born in 1923 an experienced the annexation firsthand.
The scholars like Professor Ireland and Professor Choi who were in the Korean Peninsula during the annexation are far more credible to me than a brainwashed Korean naionalist like Tae-sik Yang.
https://koreasparkling.wordpress.com/2017/06/07/reading-in-korea-with-marquis-ito-hirobumi-1907/
A Japanese on Korea 
After the end of WWII, the anti-Japanese brainwashing began in South Korea. Our first president (the military dictator) Syngman Rhee massacred hundreds of thousands, if not millions, of us. In order to cover up his atrocities and maintain legitimacy, he needed a common enemy, and Japan was an easy target. So he started the anti-Japanese brainwashing in schools and in the media.
Nobody loves anyone who hates him/herself. We Japanese hope Japan will break the diplomatic relation with Korea.