The Republic of Korea’s New Leader and Japan

Will Cooperation Continue? Maybe

By Takuya Nishimura, APP Senior Fellow, Former Editorial Writer for The Hokkaido Shimbun. The views expressed by the author are his own and are not associated with The Hokkaido Shimbun.
You can find his blog, J Update here.
June 9, 2025. Special to Asia Policy Point

A major question in Japan is whether Japan can get along with South Korea’s new progressive leader, LEE Jae-myung, who once called Japan an “enemy country.” At present the Japanese government has no explicit differences with Korea’s Democratic Party (KDP). The KDP has so far avoided discussing Japan, especially on the history issues that have long divided the two countries. The current optimism about relations between the two countries reflects changes in each country’s domestic politics and national security policies. The history issues have not been resolved, however.

It is broadly recognized in Japan that the bilateral relationship between Japan and South Korea improved under the leadership of YOON Suk Yeol, Lee’s predecessor. Yoon was, however, impeached after his abrupt declaration of martial law last December. Yoon’s decision to compensate Koreans for wartime forced labor without seeking contributions from Japanese corporations silenced conservatives in Japan who had advocated for a hard line against Korean progressives. The greatest concern in Japan now is that Korea may go back to the time before Yoon – and reopen old wounds.

Lee refrained from negative remarks about Japan in his presidential campaign. Right after his victory, he even suggested that he would maintain the bilateral relationship forged by Yoon. “Policy coherence is especially important in managing relations between nations,” Lee said on the day he was sworn into office.

The Trump Administration’s tariff policy necessitates that South Korea make common cause with Japan. Moreover, to deal with North Korea, which is expanding its missile and nuclear capability and enhancing its ties to Russia, Lee will pursue “pragmatic diplomacy:” adjusting Korea’s foreign policies to account for the latest developments in international affairs. Japan and the U.S. are likely to be at the heart of Lee’s approach.

The Prime Minister of Japan, Shigeru Ishiba, congratulated Lee on his victory. “This is the year of 60th anniversary from diplomatic normalization between Japan and South Korea, and I want to vitalize exchanges including non-governmental relationship. Enhancing cooperation between Japan and South Korea, or with the U.S., has a significance, as Japan shares such common issues as low birth rate, demographic concentration to the capital, and an alliance with America,” Ishiba said. He hopes for early meeting with Lee in the nature of “shuttle diplomacy.”

Ishiba and Lee had a telephone talk on June 9, in which Ishiba said he hoped to promote bilateral relations between Japan and South Korea based on the common ground the both countries had built. Both leaders emphasized the importance of cooperation in their bilateral relations, or their trilateral one including the United States, given the severe strategic environment.

Ishiba’s observations about common – and troubling – demographic conditions warrant serious attention. With respect to low birth rates, according to the Vital Statistics of Japan, the fertility rate (the number of babies that a woman delivers in her lifetime) was 1.15 in 2024, a year in which Japan hit a record low with fewer than 700,000 births. The situation is even more dire in the South Korea, which has the lowest fertility rate in the world: 0.75 in 2024. As to population trends, the capitals of Japan and the ROK are expanding at the expense of rural areas. Tokyo recorded the greatest population increase in 2024, while most of the other prefectures lost residents. In South Korea, half of the population lives in Seoul.

Beyond demographics, Japan and South Korea have common national security interests, which bring the United States into the picture. To protect its security environment, which is affected by the Russian invasion of Ukraine, and to protect against China’s advances, Japan has been reinforcing its multilateral arrangements for security cooperation with like-minded countries in the region.

The security frameworks of both Japan and South Korea are based on alliances with the U.S. In his policy speech to the Diet last January, Ishiba extolled the leadership of Japan and the U.S. in building multi-layered regional security networks, including the Japan-U.S.-India-Australia, Japan-U.S.-South Korea and Japan-U.S.-Philippines. For South Korea’s part, Lee said that he would “pursue pragmatic diplomacy with neighboring countries and boost trilateral Seoul-Washington-Tokyo cooperation.”

Bilateral relations between Japan and South Korea fell to their lowest point since World War II under the respective leaderships of Shinzo Abe in Japan and Moon Jae-in South Korea. That fall stemmed in large part from Abe’s revisionist view on history issues. Specifically, on the mobilization of “comfort women,” Abe in 2007 denied that Japanese officials had engaged in “coercion in narrow definition,” while emphasizing that brokers (that is, parties outside the government) had conducted “coercion in broad definition.”

Although Moon’s predecessor, Park Geun-hye, agreed with the Abe administration on a “final and irreversible” settlement of the comfort woman claims in December 2015, Moon was skeptical about the validity of the agreement. In fact, the relevant document was unique, unsigned, and unratified and existed only as two different “announcements” at a “joint press occasion.” In the absence of a conventional agreement, South Korean courts have continued to order Japan to compensate Korea’s former comfort women.

Yoon and Fumio Kishida ended the personal rivalry between the leadership of the two countries. However, domestic developments may cause Lee to take a hard line on the comfort woman issue. Even the dispute over wartime forced labor can reappear, if potential frustration against Japan grows among the people in South Korea. In 2018 and 2023, South Korea's Supreme Court dismissed the argument of Japanese corporations that compensation over the wartime forced labor was all settled.

Both countries also continue to dispute control over Takeshima Island (Dokdo in Korean). Meaningful cooperation with South Korea on national security matters will require the Ishiba administration to settle decades-long disputes over compensation of World War II comfort women and the conflicting territorial claims.