Koizumi’s First Trip to Seoul: A Sign of Cautious Japan-South Korea Reconciliation

Japanese Defense Minister Koizumi Shinjiro paid a two-day visit to Seoul on June 27-28 and held direct talks with his counterpart Ahn Gyu-back. This was Koizumi’s first official trip to South Korea in his current position, reciprocating Ahn’s visit to Tokyo in January. For the two leaders personally, it marked their fourth face-to-face meeting since last November, out of six encounters to date in total. Unprecedentedly, the two ministers jointly visited South Korea’s Black Eagles aerobatic team at the Wonju Air Base. It was the first time a foreign defense minister had done so.

The last visit similar to Koizumi’s recent trip was in September 2025, when then-Japanese Defense Minister Nakatani Gen traveled to Seoul to meet his South Korean counterpart Han Min-koo. While Nakatani’s visit symbolized the end of a decade-long diplomatic hiatus between the two countries, the latest talks also marked a significant milestone for their relations. It was the second time in history, repeated after 23 years, that Japanese and South Korean defense ministers have exchanged visits within a single year.

Beyond its symbolic meaning, Koizumi’s rare talks with Ahn in Seoul also signaled the steady strengthening of high-level bilateral defense cooperation between the neighbors. Previously, on May 7, Japan and South Korea held their first “2+2” vice-ministerial talks between their foreign and defense ministries in Seoul, marking an upgrade from the original director-general level launched in 1998. Koizumi’s trip also came just weeks after Tokyo and Seoul resumed joint maritime search-and-rescue exercises (SAREX) following a nine-year hiatus. These signs indicate a remarkable normalization of cooperation between the two countries’ defense authorities since the 2018 incident involving a South Korean naval vessel and a Japanese Maritime Self-Defense Force patrol plane.

The joint statement released after the talks said the two sides would continue developing cooperation between their aerobatic teams (Blue Impulse and Black Eagles). This was considered an important step forward, given that Japan had previously refused to provide refueling support for the Black Eagles in November 2025 due to the Dokdo/Takeshima territorial dispute; one of the aircraft in the Black Eagles had taken part in a drill over the islets. Although this does not necessarily imply that South Korean military aircrafts will receive refueling support from Japan regularly, it remains a notable detail, as the disputed islets have long been a major obstacle in bilateral relations.

The two ministers also reaffirmed their commitment to “complete denuclearization of the Korean Peninsula and permanent peace” in the region during their talks, just one day after a joint China-Russia air drill near the peninsula. As the United States has repeatedly demanded greater burden-sharing from its allies, including Japan and South Korea, this conveyed a clear message: Tokyo and Seoul are advancing a closer military coordination to proactively address their common security challenges in Northeast Asia, such as North Korea’s nuclear program, Russia-North Korea military cooperation, and Beijing’s military buildup.

What drew the most attention, however, was the absence of any mention of concluding an Acquisition and Cross-Servicing Agreement (ACSA), a military logistics support pact that Tokyo had long sought to sign with Seoul. Japan pursued the ACSA with South Korea’s Lee Myung-bak administration in 2012, but the deal faced strong public disapproval in South Korea. Lingering public unease over the ACSA centers on the concern that it would pave the way for the deployment of Japanese forces on South Korean territory.

However, ACSA talks between the two countries have re-emerged over the last months amid growing uncertainties in the regional security environment. If signed, a Japan-South Korea ACSA would enhance interoperability and facilitate joint activities between the two forces, particularly in emergencies when U.S. forces in Japan and South Korea require logistical support.

Such prospects, however, will not be easy to realize. Seoul is proceeding with caution, viewing the issue as politically sensitive, especially since the scope of cooperation under the ACSA could expand over time. On the one hand, this requires public understanding in South Korea, where historical resentments of Japanese colonial rule from 1910-1945 remain unhealed. On the other hand, Seoul must avoid being drawn into Japanese military activities led by the U.S. in the broader region beyond the Korean Peninsula, as Beijing or Pyongyang could interpret this as Seoul deliberately tightening trilateral cooperation with Washington and Tokyo. The consequences would be detrimental for South Korea, particularly when the Lee Jae-myung administration is trying to maintain balanced relations with the U.S., Japan, China, and Russia to secure support for resuming talks and improving ties with Pyongyang.

Overall, the latest defenseminister talks once again demonstrated Tokyo and Seoul’s consistent commitment to building a “future-oriented partnership,” as agreed by the two heads of state. With the current frequency of intensive “shuttle diplomacy,” reciprocal visits and regular defense talks between Japan and South Korea are expected to continue, at least under the current administrations.