By actively propelling policies that would strengthen the ties between the United States and Japan by means of revising US-Japan policies, the Abe regime has recently increased its right for collective self-protection. By closely examining the trend in the US-Japan alliance and its future directions, the Republic of Korea (ROK) should prepare for upcoming changes. First, the ROK government should establish and develop its policies toward Japan under the presupposition that Japan is both “common nation” and “nation of great military power.”Second, attentively observing the possibility of a US-Japan alliance shifting its recognition of a threat from North Korea to China, the ROK government should strategically approach ROK-Japan and ROK-US-Japan cooperation. Third, the ROK government should analyze the competition over power in Northeast Asia between Japan and China based on alliances with the United States and its impact on the security of Korea is necessary. Fourth, even though disparate perceptions of historical events still exist between the ROK and Japan, as an effective measure toward issues such as North Korean nuclear missiles and the currently unstable security environment of Northeast Asia, there is a need for ROK government to make a prudent and yet positive approach toward reopening talks and resuming cooperation with Japan.