This chapter examines the struggle for social justice among Koreans in Japan. Examining policy debates in Japan from its imperial-colonial period to contemporary global manifestations reveals how the dissemination of human rights into legal practices facilitates the expansion of citizenship rights among certain immigrants, but reproduces categorical inequalities among marginalized groups. This development is driven by a complex interplay of inter-state political interests, minority’s social movements, historical redress, and power imbalance between Japan and the immigrants’ respective homeland states. Paradoxically, while endogenous and exogenous factors engender the expansion of citizenship, cosmopolitanization may also contribute to proliferation of inequalities between old and new immigrants. The chapter contributes to our understanding of Korean activism and their pursuit of social justice in Japan’s complex sociopolitical landscape.