The competition between the U.S. and China in the Indo-Pacific region significantly impacts ROK's national security. In this context, ROK should find clues about setting up ROK-US relations, ROK-China relations, and inter-Korean relations. This article aims to explore the clues using international relations theories for the future of South Korea. Thus, this article found three main implications for achieving South Korea national security. In terms of realism, the ROK-U.S. alliance must be strengthened to pursue security and stability in the region. In terms of liberalism, ROK must maintain a cooperative relationship with China. In terms of constructivism, Inter-Korean relations should be fostered with the goal of recognition of the other party through meetings and negotiations.