This dissertation examines the early-twentieth-century evolution of family law in the Japanese empire. Contrary to popular perceptions of Japan as uniformly patriarchal, I identify a progressive turn that promoted intimacy-based family life in court cases involving concubines and illegitimate children in Japan, Taiwan, and Korea. After World War I, the principal thrust of Japanese family law shifted from preserving patrilineage to protecting the best interests of the child. This momentum continued through the 1930s and inspired a series of legal reforms that defied the conservative backlash of total war mobilization. The change in Japanese family law mirrored a global transformation of the family from being part of a broader kinship network to constituting the emotional core of an individual’s life. Japan’s experience offers a unique vantage point for understanding family regulation. Historians of western empires have emphasized the management of women as a crucial means of distinguishing the colonizer from the colonized. They have also argued that competition between colonizers and indigenous elites over defining gender hierarchies reinforced patriarchal values. This cannot, however, account for the steady movement toward egalitarian, affective families in the long twentieth century. Through the prism of the Japanese empire, this dissertation illustrates how this movement, which originated in universal human aspirations for intimacy and happiness, transcended national interests and imperial borders.