According to the article President Moon is only doing this to try and promote his North Korea engagement policies during the Summer Olympics like he did during the last Winter Olympics:

President Moon Jae-in’s rush to resolute serious issues with Japan before the Tokyo Olympic Games is not going as well as Cheong Wa Dae had hoped.
Moon named former four-term ruling party lawmaker Kang Chang-il as the next ambassador to Japan last month. It was the first time he had named a politician to the post, after first appointing Lee Su-hoon, an international relations professor, and then Nam Kwan-pyo, a career diplomat and one of the foremost experts on Japan at the Ministry of Foreign Affairs.
Nam has served as the Korean ambassador to Japan since May 2019. It is considered rare for the envoy to Japan to be replaced less than two years after being appointed. Cheong Wa Dae said that sending a politician to the post has a particular meaning amid the deadlock in bilateral relations.
“With the launch of the new Cabinet in Japan, it reflects the President’s determination to find a resolution to the problems in bilateral relations,” a senior presidential aide said. “Kang served as head of the Korea-Japan Parliamentarians’ Union and has built an extensive network in Japan. Based on this, we determined it would be more suitable to send a politician rather than a career diplomat.” (……..)“One major factor in the Moon administration’s renewed push to improve relations with Japan is the possibility that doing so will allow the Tokyo Olympics to serve as a potential showplace for a breakthrough with North Korea,” Mason Richey, associate professor of international politics at Hankuk University of Foreign Studies in Seoul, told The Korea Times.
Korea Times
You can read more at the link, but I don’t see the Japanese wanting to do the Moon administration any favors considering all the anti-Japanese policies and rhetoric they have pushed the past few years.








