Japan is sending its foreign minister, Yoshimasa Hayashi, to South Korea Yoon's inauguration on Tuesday.
He was due in Seoul today, and Tokyo's foreign ministry says Hayashi will be meeting with key members of the incoming government.
Japanese media said he was expected to meet today with foreign minister nominee Park Jin, and is arranging a separate meeting with Yoon himself to deliver a letter from Japanese Prime Minister Fumio Kishida.
This will be the first visit to Seoul by a Japanese foreign minister since Taro Kono's visit in June 2018.