Japan has responded to the pressure of the PLA navy and air force frequent passing through Miyako waterway by strengthening its military build-up in the southwestern islands. That said, Japan's actions, in essence, is counter China's military threat. Japan's military construction has been evolving in the context of US-China competitions, with the coexistence of challenges and opportunities. Japan uses the opportunity of U.S. strategic shift to "Indo-Pacific Strategy" to enhance the capability of JSDF in the southwestern islands that ensure the security of the SLOC. In the meantime, Japan is also to share more security responsibility. Japan's military deployment at the southwestern islands does not only meet the purpose of "Indo-Pacific Strategy" and reflect Taiwan's geographical strategic values but also give Taiwan's government takes this opportunity to enhance her security cooperation with the US and Japan in the first island chain.