Japan-PH relations: Toward a ‘quasi-alliance’
Security cooperation with the Philippines has become even more important for Japan as it seeks to realize a free and open Indo-Pacific, and maintain peace and stability in East Asia.
Japan has deepened its security cooperation with the Philippines by holding 2+2 foreign and defense ministerial meetings, signing the Reciprocal Access Agreement (RAA), selling it an air surveillance radar system, and providing it patrol boats. Prime Minister Shigeru Ishiba’s visit to the Philippines in April 2025 further accelerated this trend.
In the summit meeting with President Marcos, Ishiba noted that Japan and the Philippines are both US allies and share fundamental values. Marcos noted that “the two countries are now in a golden age,” and expressed his intention to promote cooperation in several areas to further strengthen their strategic partnership.
Japan and the Philippines face a common security challenge as China’s attempts to change the status quo through force and coercion. In the East China Sea, China Coast Guard (CCG) vessels have repeatedly intruded into Japan’s territorial waters around the Senkaku Islands and are stepping up actions that threaten Japan’s sovereignty.
In the South China Sea, CCG vessels have repeatedly engaged in dangerous actions such as spraying water and ramming Philippine Coast Guard (PCG) patrol vessels. Ishiba and Marcos discussed such aggression and “confirmed their opposition to unilateral attempts to change the status quo by force.”
This Japan-Philippines Summit unfurled two major developments in the security cooperation between the two countries. First, they agreed to begin negotiations on an Acquisition and Cross-Servicing Agreement (ACSA). The ACSA is an agreement for the mutual provision of goods such as food, fuel, and ammunition, and services such as transportation and medical care between the two countries. This allows the Japan Self-Defense Forces (JSDF) and the Philippine military to share resources when conducting joint military exercises. Together with the RAA, already signed and in the process of taking effect, this is seen to lead to the strengthening of cooperation between the JSDF and the Philippine military.
The second development is the two countries’ agreement to start discussions on the early conclusion of an “Information Security Agreement.” Commonly known as the General Security of Information Agreement (GSOIA), it commits two countries into sharing military information which are confidential and won’t be shared with third countries. If an information security agreement is concluded between Japan and the Philippines, it will be possible for the JSDF and the Philippine military to share information on the activities of the Chinese military and the CCG.
If Japan, which collects a lot of information in the East China Sea and the Pacific Ocean, and the Philippines, which focuses on collecting information in the Bashi Channel and the South China Sea, were to exchange such military information, it is expected that the situational awareness capabilities of both countries in the seas and airspace of East Asia will be greatly enhanced.
Reacting to this result, Ishiba pointed out in a joint press conference that “Japan and the Philippines have become partners close to an alliance.” Facing a common security challenge in China’s aggressive maneuvers has deepened the cooperation between Japan and the Philippines, enhancing mutual security to maintain regional peace and stability. The relationship between the two countries is approaching a level that can be described as a “quasi-alliance.”
Strengthening security cooperation toward a quasi-alliance between Japan and the Philippines will also lead to stronger cooperation with the United States, their common ally, and will improve the deterrence of Japan, the United States, and the Philippines against China.
Coinciding with Ishiba’s visit to the Philippines, the US and Philippine militaries held the Balikatan 2025 multilateral military exercise, where the US military deployed its most advanced land-to-ship missile, NMESIS, in the northern Philippines overlooking the Bashi Channel. The focus is how to deal with China.
For its part, the JSDF, which had previously participated in the Balikatan exercises as observers, sent the frigate JS Yahagi and joined the actual exercise for the first time. Australia, which is said to have a “quasi-alliance” with Japan, also sent troops to participate in Balikatan 2025.
Strengthening security cooperation between Japan and the Philippines will further deepen cooperation among regional countries committed to upholding the rule of law, and a rules-based international order.
Masafumi Iida is director of the Security Studies Department, National Institute for Defense Studies (NIDS) of Japan.
