By focusing on the emergence and integration of “hybrid children” ( konketsuji ) anthropology into the Human Adaptability section of the International Biological Program (HA-IBP) in Japan during the 1950s and 1970s, this paper presents how transnational dynamics and mechanisms played out in shaping and maintaining the racist aspects while simultaneously allowed them to be included in the HA-IBP framework. It argues that Japanese anthropologists operated a double play between their national and transnational spaces, that is, they attenuated racist aspects of their research in their international activities while authenticating race in their national work. This paper will conclude with reflections on the transnational nationalism of konketsuji anthropology.