This study focuses on the phenomenon that the U.S.-Korea-Japan security triangle wasn’t reinforced but rather relaxed in the intensified competition between the U.S. and China from 2017 to 2022. This article argues that conflicting strategic interests between Korea and Japan are the primary driver of their conflict within the triangular system. Since the Cold War, Japan has maintained dominance in Korea-Japan relations, characterized by an asymmetrical dynamic between the prosperous democratic Japan and the impoverished authoritarian Korea.