Abstract: Japan is abandoning its once unidirectional foreign security policy towards the USA, two notable examples of which are its increasingly comprehensive and substantial security relations with the Philippines and Vietnam. Putting these burgeoning Japanese security partnerships front and center, this paper asks the following questions: What are the characteristics of Japan’s maturing security partnerships with the Philippines and Vietnam? What factors have driven and enabled their recent emergence? What promotes and constrains their future development? What do these maturing Japanese non-US security partnerships reveal about Japan’s direction as a security actor in and beyond East Asia? The paper finds that these two Japanese security bilaterals, which have six basic characteristics in common, are fundamentally driven by the contemporary shift in the balance of power and the strategic challenge that China’s emerging maritime power and ambitions present Japan. It moreover argues that the substantiation of these security partnerships have been pursued under American auspices and further invited by Japanese nationalism and security legislative reforms. Notwithstanding these encouraging factors, however, domestic and geo-strategic constraints and counter incentives lead this paper to expect further substantiation, but limited military significance in the future of these security partnerships.