Recent scholarship suggests that the thawing of diplomatic relations between China and Japan has caused a readjustment of Beijing's Belt and Road Initiative and Tokyo's Free and Open Indo-Pacific Vision towards an emerging complementarity. Through careful process-tracking, elite interviews, and analysis of Chinese and Japanese primary sources, this article instead demonstrates how, outside of the East Asian spotlight, Sino-Japanese geo-economic competition continues in South Asia and the Mekong subregion, fueled by power politics and a mutual distrust of each other's initiatives. On the basis of this evidence, this article qualifies Sino-Japanese interactions as a quest and denial for spheres of influence, whereas the Japanese government aims at denying Chinese spheres of influence. In doing so, this article highlights how Japanese proactivism from Sri Lanka to Thailand, via infrastructure and government financing, has become a driver of growing non-traditional security with India, the U.S., and Australia.