The Emerging Power Play in the Mekong Subregion:A Japanese Perspective Kei Koga (bio) As one of the most active development donors in Southeast Asia, Japan has committed to socioeconomic development in the Mekong subregion since the end of the Cold War. However, as the Sino-U.S. rivalry intensifies, socioeconomic development in Asia, including the Mekong subregion, has become a theater for strategic competition. In 2013, China initiated the Belt and Road Initiative (BRI), raising its economic and political influence in the region through massive development assistance. For its part, Japan launched the Partnership for Quality Infrastructure (PQI) in 2015 to boost its assistance to Asia, and Tokyo strengthened its development cooperation with like-minded partners, particularly the United States, by establishing joint frameworks such as the OPIC-JBIC-Australia agreement on development finance in 2018 and the Blue Dot Network in 2019.1 Is the Mekong subregion destined to be subsumed into a power play of China versus Japan and the United States? This essay argues that Japan does not always aim to counterbalance China's growing influence in the Mekong subregion and could even play a role to ease geopolitical tensions in the region. Although the intensified U.S.-China strategic competition narrows Japan's diplomatic space to engage China, the Mekong subregion is still a potential area for Japan-China cooperation, mitigating the negative impact of great-power rivalry. Under the condition that China meets "quality infrastructure" standards, Japan and China could explore cooperation on development policy through a working-level bilateral dialogue, the ASEAN +3 (the Association of Southeast Asian Nations members plus China, Japan, and South Korea), and the East Asia Summit. The Development of Japan-Mekong Relations Japan's development commitment to the Mekong subregion began near the end of the Cold War, when Vietnam and Laos moved to become market [End Page 28] economies in the late 1980s and the Paris Peace Accords for Cambodia were signed in 1991. To facilitate the subregion's socioeconomic development, Japan created the Forum for Comprehensive Development of Indochina in 1993 to promote connectivity, such as the Greater Mekong Subregion's East-West Economic Corridor that aimed to improve transportation and economic integration between the states. Japan's Ministry of International Trade and Industry (MITI) and the ASEAN Economic Mechanism (AEM) also established the AEM-MITI Working Group of Economic Cooperation for Indochina and Myanmar in 1994 to facilitate market economy and infrastructure development.2 After ASEAN incorporated all five Mekong subregional states as members, Japan aimed to help address the "ASEAN divide"—the large economic and development gap between the original ASEAN members and the new members, Cambodia, Laos, Myanmar, and Vietnam (CLMV). Accordingly, when Cambodia, Laos, and Vietnam (CLV) proposed the concept of a "development triangle," they successfully solicited Japan for political and financial support.3 The countries then created the Japan-CLV framework, through which they held summits and foreign ministers' meetings annually from 2006 to 2008 to discuss subregional development schemes. From 2007 onward Japan's socioeconomic focus began to shift when it launched the Japan-Mekong Region Partnership Program. The program has three pillars: (1) economic integration, (2) trade and investment expansion, and (3) "universal values" and common goals, particularly the Millennium Development Goals.4 Japan then expanded its official development assistance (ODA) to the region and conducted negotiations for bilateral investment agreements with Cambodia and Laos, respectively. This Japan-Mekong framework was rapidly institutionalized through regular foreign ministers' meetings from 2008 and summits from 2009. The framework also gradually incorporated discussions over regional strategic [End Page 29] issues, such as the management of China's rapidly growing influence in the Mekong subregion.5 In 2010, Japan's intention to shape the subregional order based on existing international rules and norms grew clearer. It used the Japan-Mekong cooperation framework as a steppingstone for this agenda, corresponding with the U.S. "rebalancing" strategy and the Lower Mekong Initiative (LMI). To be sure, Japan still emphasized socioeconomic development as a top priority. The Tokyo Strategy 2012, which was issued during the 4th Mekong-Japan Summit and encapsulated three-year cooperative guidelines, aimed to build connectivity through infrastructure development, improve the investment environment...