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, following Ahn’s visit to Tokyo in January. For the two leaders personally, this was their fourth face-to-face since last November, out of six meetings in total to date. In an unprecedented move, the two ministers jointly visited South Korea’s Black Eagles aerobatic team at Wonju Air Base. It was the first time a foreign defense minister had done it.
The last visit similar to Koizumi’s recent trip was in September 2025, when then-Japanese Defense Minister Nakatani Gen visited Seoul to meet his South Korean counterpart Han Min-koo. While Nakatani’s visit symbolized the end of a decade diplomatic break Between the two countries, the latest negotiations also marked an important step for their relations. It was the second time in historyrepeated 23 years later, that Japanese and South Korean defense ministers exchanged visits in the same year.
Beyond their symbolic significance, Koizumi’s rare talks with Ahn in Seoul also marked the steady strengthening of high-level bilateral defense cooperation between the neighbors. 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 improvement from the initial 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) after a nine-year hiatus. The signs point to a remarkable normalization of cooperation between the two countries’ defense authorities since the 2018 incident involving a South Korean navy ship and a Japan Maritime Self-Defense Force patrol aircraft.
The joint communiqué published at the end of the negotiations indicates that the two parties will continue to develop cooperation between their aerobatic teams (Blue Impulse and Black Eagles). This was seen as an important step forward, given that Japan had previously denied provide refueling support to the Black Eagles in November 2025 due to the Dokdo/Takeshima territorial dispute; one of the Black Eagles planes had participated in an exercise over the islets. While this does not necessarily imply that South Korean military aircraft will receive regular refueling support from Japan, it is still a notable detail, as the disputed islets have long been a major obstacle to 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 a day after a joint Sino-Russian air exercise. near the peninsula. While the United States has repeatedly demanded greater burden-sharing from its allies, including Japan and South Korea, it has sent a clear message: Tokyo and Seoul favor closer military coordination to proactively address their shared security challenges in Northeast Asia, such as North Korea’s nuclear program, military cooperation between Russia and North Korea, and Beijing’s military buildup.
But what attracted the most attention was the absence of any mention of the conclusion of an Acquisition and Cross-Services Agreement (ACSA), a military logistics support pact that Tokyo had long sought to sign with Seoul. Japan pursued ACSA with the South Korean administration of Lee Myung-bak in 2012, but the agreement faced difficulties. strong public disapproval in South Korea. Lingering public unease with the ACSA centers on fears that it will pave the way for the deployment of Japanese forces into South Korean territory.
However, ACSA talks between the two countries have resurfaced in recent 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 need logistical support.
However, such prospects will not be easy to achieve. Seoul continues cautionconsidering the issue politically sensitive, especially as the scope of cooperation under the ACSA could expand over time. On the one hand, it requires public understanding in South Korea, where historical resentments against Japanese colonial rule from 1910 to 1945 remain intact. On the other hand, Seoul should avoid getting drawn into U.S.-led Japanese military activities in the broader region beyond the Korean Peninsula, as Beijing or Pyongyang could interpret this as a deliberate strengthening of trilateral cooperation with Washington and Tokyo. The consequences would be detrimental for South Korea, especially as Lee Jae-myung’s administration attempts to maintain balanced relations with the United States, Japan, China and Russia to gain support for resuming negotiations and improving ties with Pyongyang.
Overall, the latest discussions between defense ministers once again demonstrated Tokyo and Seoul’s continued commitment to building a “future-oriented partnership” as agreed by the two heads of state. With the current frequency of intensive “shuttle diplomacy,” regular reciprocal visits and defense talks between Japan and South Korea are expected to continue, at least under the current administrations.