This dissertation examines the policies, promoters, and patterns of Japanese-Korean marriages (naisen kekkon) and Japanese-Taiwanese marriages (naitai kyōkon) in imperial Japan. It seeks to answer why the Japanese empire sanctioned intermarriage when the Euro-American empires condemned marriage between colonizers and colonized subjects in the twentieth century. It also questions who were the people that promoted intermarriage and why people intermarried in Japan, where the government legalized intermarriage but did not promote it at the national level. This research further investigates what happened to people who intermarried before 1945 in postwar Japan, and why so little is known about the history of Japanese-Korean and Japanese-Taiwanese marriages in contemporary Japan. With existing studies on the history of intermarriage in the Japanese empire focusing on colonial Korea and Taiwan, this project focuses on Japan. Through analysis of internal and external influences on the discourse of intermarriage in the metropole, it first argues that imperial Japan’s sanctioning of intermarriage was based on its population policies and observations of its contemporaneous empires, thus should not be equated with the absence of racism in Japan and its isolation from the world. It then reveals that intermarriage was promoted in Japan at the local level by the members of the Harmony Association (Kyōwakai), district commissioners (hōmen’iin), and Japanese women. By studying the history of Japanese-Korean and Japanese-Taiwanese marriages together rather than separately, this research demonstrates the limitation of relying on categories such as “colonizer” and “colonized” alone in understanding the promoters and patterns of intermarriage, and proposes consideration of a/sexuality and ability in addition to race/ethnicity, gender, and class when studying colonizer-colonized relationships in modern empires. Lastly, this research traces the history of intermarriage post-1945 to reveal the existence of Japanese-Korean and Japanese-Taiwanese couples in postwar Japan and argues that it has been selectively remembered. Engaging with scholarship in modern Japanese history, imperial and colonial studies, and gender and sexuality studies, this dissertation ultimately makes a case for a more inclusive history that includes into history those who are marginalized in, excluded from, and/or forgotten in existing mainstream frameworks of history, to explain contemporary social issues of historical origin, such as disavowal of racism, in hopes of making a positive social change.