This paper elucidates the purpose behind the re-entry permission granted by the Minister of Justice in Japan to Zainichi Koreans who had Chosen (in English the Korean peninsula) nationality. By analyzing the complex triangular relationship among Japan, the Republic of Korea (ROK), and the Democratic People’s Republic of Korea (North Korea), this study elaborates that the key objective in Japan’s unprecedented re-entry permission was to adjust its policy to a new legal and political situation during the détente. With the beginning of normalization talks between Japan and South Korea, the Japanese government permitted re-entry for Kankoku (in English South Korea) nationality holders, who were eligible to obtain a South Korean passport, considered a valid passport in Japan. However, Chosen nationality holders, who were regarded as pro-North Korean by both countries and who could not possess a valid passport, were denied re-entry to Japan. By strictly controlling Chosen nationality holders, these countries attempted to maintain its relationship. However, in the late 1960s, Japan was faced with a legal and political dilemma and had no option but to permit pro-North Koreans to re-enter Japan. This paper argues that this permission was Japan’s political compromise to guard against its diplomatic isolation in a structural shift away from the confrontation of the Cold War.