Japan wants a more united and proactive Southeast Asia as it sees Asean as a bulwark against an intensifying great-power rivalry, analysts say, while uncertainty over Washington’s long-term Indo-Pacific strategy has deepened Tokyo’s concerns about the region’s future.

Japanese Defence Minister Shinjiro Koizumi on Wednesday urged Southeast Asian nations to strengthen their collective response to emerging security threats, warning of a “rapidly deteriorating” security environment and shifts in the regional military balance that raised the risk of “dangerous miscalculations”.

“These crises do not merely adapt. They overlap and amplify one another,” Koizumi said at the Asean-Japan Defence Ministers’ Informal Meeting in Cebu.

He urged the Association of Southeast Asian Nations to protect its unity, centrality and resilience, and said the bloc must be able to overcome differences and set its priorities while acting on a common agenda with external partners.

“Unity means working together despite differences. Centrality means setting the region’s agenda and drawing external partners around it. Resilience means keeping essential functions and autonomy intact in a crisis,” Koizumi said.

The defence minister also proposed updating cooperation between Japan, Asean and partners outside the bloc in emerging security areas such as artificial intelligence technology, unmanned systems, and the protection of critical undersea infrastructure. “When challenges change, cooperation must change with them,” he said.

Koizumi’s remarks reflect Japan’s perception of Asean as a theatre for greater strategic rivalry, as well as an anchor that enables practical cooperation across the region, observers say.

“Koizumi’s remarks show that Japan sees the regional balance shifting structurally against the status quo and fears that grey-zone coercion could escalate through miscalculation,” Sarah Soh, an associate research fellow at the S. Rajaratnam School of International Studies, told This Week in Asia.

“Against this backdrop, Japan sees Asean as a normative anchor, as an inclusive platform that keeps all major powers engaged, and as a partner for practical cooperation.”While Koizumi shared Japan’s assessment of a deteriorating regional security environment, with implicit references to China, his speech “focused largely on expanding practical cooperation and building regional resilience in disasters, supply chains, and energy, alongside a reaffirmation of Asean unity and centrality”, Soh said.

“On balance, the speech strikes a measured tone and is unlikely to unsettle Asean member states.”Satoru Nagao, a non-resident fellow at Hudson Institute, said Asean could become a theatre for a US-China power game, much like Central Europe during the US-Soviet Cold War.

“Today, Southeast Asia lies between the US and China and is made up of many small countries. This means it could become the ‘Central Europe’ between the US and China,” the Tokyo-based Nagao said, adding that the scenario highlighted the importance of Asean unity.

Don McLain Gill, an international relations lecturer at De La Salle University, agreed that it was in “the best interests of Japan to have a more resilient, aware and proactive Southeast Asia” amid the backdrop of uncertainty over Washington’s long-term strategy for the Indo-Pacific.

“For Japan, it would do its best to encourage Southeast Asia to begin thinking more proactively about its future and how its members need to work together to maintain the status quo, according to international law,” Gill said, adding that Japan could serve as an anchor and a reliable partner for the region in keeping the order intact.

Collin Koh, a senior fellow and coordinator of naval and maritime affairs projects at the S. Rajaratnam School of International Studies’ Institute of Defence and Strategic Studies, said Koizumi’s remarks reflected Japan’s long-standing interest in Southeast Asia, adding that the rhetoric was an enduring one for Tokyo.

“It is essentially an emphasis on the interdependence across the subregions of the Indo-Pacific. And that, of course, pertains to Southeast Asia alongside Northeast Asia,” Koh said.

While Koizumi emphasised the need for Japan-Asean defence cooperation, Tokyo “would be quite cognisant of the fact that Southeast Asia itself is not a monolithic body”, Koh noted.

“Asean is far from a monolithic body with the sort of institutions that will enable much closer defence and security cooperation between Japan and Asean as an institution itself,” Koh said, noting that more concrete measures would usually happen at the bilateral and minilateral levels.

Regarding Japan’s proposal to boost cooperation with Asean and other external partners in emerging security areas such as AI, unmanned systems and sea cables, analysts warn that Asean may not be able to match Japan’s capacity.

Asean was likely to welcome the idea as it shared Japan’s concerns in these areas, but could frame the cooperation as building resilience rather than deterrence and move cautiously on involving external partners, Soh said.

“Most member states also lack the technology and experience to protect undersea cables or use AI and unmanned systems at scale. Asean is therefore likely to support Japan’s direction in principle but proceed slowly, with practical progress depending largely on Japanese support and technology,” she said.

While Japan had not developed its own capabilities well in AI and unmanned systems, it excelled in its technology for undersea cables, Nagao said.

“Japan’s concern is China’s domination in these areas because of the cost of AI and unmanned systems,” Nagao said, adding that Tokyo could leverage its goodwill in the region from having made several investments to improve Southeast Asia’s capabilities.

Koh said undersea cable infrastructure remained a vulnerability for the region and could be the most relevant area of Japan-Asean cooperation.

“In a way, Southeast Asia is a gateway and interconnection between the world’s oceans where those undersea cables pass through. So certainly it gives Asean a certain advantage purely due to geography,” Koh said.

However, individual countries’ capacities varied widely, making it difficult to establish a framework to bring member states together “largely because not all of them might be able to offer anything substantial to the table”, Koh said.

“So it could well be a pretty lopsided type of contribution where they might be sidelined for the most part,” Koh said, but remained hopeful that any initial discussions could “spawn off more substantial cooperation thereafter”.