This paper examines Motomori Kimura’s (木村素衛 1890–1946) educational theory through an analysis of his 1941 wartime lecture on national schools, set against the backdrop of Japan’s Greater East Asia Co-Prosperity Sphere. Utilizing central concepts from Kimura’s 1939 work—the expressive world, the historical world, and the public world; self-mediation; and formation—this study explores how individual and national subjects are constituted through cultural negotiation and engagement with others. This analysis shows that Kimura’s framework supports possibilities for universal coexistence and mutual transformation, thus challenging prevailing nationalistic paradigms. By highlighting cosmopolitan elements that persist even in restrictive wartime contexts, this paper offers new insights into international educational research. It advocates for a historical re-examination of global citizenship and intercultural dialog within educational philosophy, emphasizing the contemporary relevance of Kimura’s ideas for ongoing discussions of cosmopolitanism and transnational education.