Japan is increasingly positioning itself to become Indonesia’s primary strategic partner in the Indo-Pacific region. Over the past 12 months, the two nations have substantially deepened bilateral cooperation in defense and energy, among other long-term strategic sectors beyond trade and investment.

As strategic competition intensifies throughout Southeast Asia, Indonesia is seeking partners that can strengthen its security and economy while respecting its non-aligned foreign policy. Meanwhile, Japan is seeking to take on an expanded role as a regional security provider that complements its existing economic presence in Southeast Asia. Put together, these converging interests highlight how the Indonesia-Japan relationship is entering a new phase defined by long-term strategic partnership.

The strategic interests of both Indonesia and Japan complement each other well. Indonesia’s current status as Southeast Asia’s largest economy, its control over the Malacca, Sunda, Lombok, and Makassar straits, and its abundant natural resources all synergize well with Japan’s expertise in defense, manufacturing, and emerging technologies.

However, this growing relationship faces a variety of challenges on both sides. Political uncertainty in both countries, including declining approval ratings for Japanese Prime Minister Takaichi Sanae, economic uncertainty in Indonesia, and the arrest of Indonesia’s top anti-corruption prosecutor, could complicate long-term policymaking.

Public opinion also poses a challenge, with some Indonesians having seen Japan as being too closely aligned with the United States. This raises questions about whether deeper cooperation between Indonesia and Japan is compatible with Indonesia’s long-standing non-aligned foreign policy.

For Japan to become Indonesia’s principal Asian partner, Tokyo must demonstrate that increased cooperation strengthens Indonesia’s national sovereignty and strategic flexibility.

Defense cooperation has become the most visible expression of this expanding partnership. On June 7, authorities from both countries agreed to begin discussions on the export of Japan’s older Asagiri-class destroyers to Indonesia. Just one month before, Indonesia and Japan signed a defense cooperation agreement that included the possible acquisition of Japanese submarines and the newer Mogami-class stealth frigates to Indonesia.

This momentum has also included wider regional security initiatives. In early 2026, Indonesia, Australia, and Japan signed a trilateral security cooperation agreement, with Indonesia specifically bolstering facilities on Morotai Island in eastern Indonesia which Japan and other partners could access for training. For Indonesia, this opportunity offers the archipelagic nation access to advanced platforms, training, and strategic support without formally abandoning its neutral posture, while for Japan, this would create an opportunity to contribute to regional security through capacity-building and interoperability.

Energy security has also become a key pillar of the growing relationship between Jakarta and Tokyo. Indonesia’s desire to diversify its energy mix bodes well with Japan’s need for reliable long-term energy partners. Both governments have recognized the importance of coordinating energy policies and cooperation agreements, enabling both nations to ensure continuous fuel to ensure reliable energy supplies for long-term economic growth.

On April 19, Indonesia and Toyota announced talks on a potential joint investment in Indonesia-based bioethanol production. This news followed the announcement that Indonesia and Japan had agreed to boost cooperation in the economic and security realms, with both countries also agreeing to coordinate further on topics related to energy security owing to the ongoing U.S.-Iran war.

Furthermore, this cooperation is increasingly extending beyond conventional energy security into the long-term transition toward clean and resilient energy systems, with Indonesia having a desire to create up to 500 MWe of nuclear capacity by 2034. In mid-March 2026, Indonesia and Japan signed a memorandum of cooperation focused on developing nuclear energy technologies and ensuring the critical minerals supply chain.

This came shortly after both countries, alongside the U.S., held a conference on developing small modular reactors (SMRs) to strengthen cooperation on nuclear energy. The three countries discussed supporting Indonesia’s long-term clean energy and energy security goals, reinforcing its role as a regional leader in nuclear reactor development. Previously, Indonesia received assistance from the U.S. State Department’s civil nuclear energy security assistance program, while also working with Oregon-based NuScale in early 2023 on deploying an SMR facilitated by a grant via the U.S. Trade and Development Agency.

Altogether, these initiatives suggest that nuclear cooperation could evolve into one of the key parts of the Indonesia-Japan relationship. This would also coincide well with Japan’s desire to ensure its own security via nuclear energy, to generate 20 percent of its energy from nuclear sources by 2040.

Indonesia and Japan have also launched cooperation efforts in a variety of other areas, spanning everything from public health to economic cooperation. For example, on June 5, Japan and the World Health Organization announced an initiative to tackle Indonesia’s existing immunization gaps.

This news was preceded by the April 2026 announcement of Indonesia and Japan agreeing to cooperate on carbon investment as well as facilitate knowledge exchange specific to forestry and conservation. Around the same time, the government-affiliated Japan External Trade Organization hosted a Japan-Indonesia Business Forum with the Indonesian Chamber of Commerce and Industry in Tokyo to facilitate further economic cooperation, including investment partnerships specific to Indonesia’s sovereign wealth fund, Danantara.

Previously, in late 2025, Indonesia and Japan signed a cooperation agreement focusing on the utilization of local currencies for all bilateral transactions, reducing transaction costs and exchange risk while also boosting bilateral trade and investments.

Japan’s expanding engagements with Indonesia represent a broader effort at redefining its current strategic role in Southeast Asia. For Indonesia, closer ties with Japan offer it a chance to strengthen its defense, energy, and economic sectors without abandoning its commitment to strategic non-alignment.

The success of Japan’s desire to become Indonesia’s primary partner in Asia will depend on whether Tokyo’s efforts help support Indonesia’s goal of strategic autonomy. If such a balance can be sustained, an Indonesian-Japan partnership could become one of the most important in the region in the coming years.