This article examines the thought and career of Nabeyama Sadachika (1901-79) from communist militant in 1920s Japan to his conversion to the emperor system in the 1930s and, finally, to his role in shaping the postwar anti-communist movement. Using Nabeyama's recently released private papers, the article shows how he brokered his anti-communist expertise to a range of postwar actors and institutions-the police, the Self-Defense Forces, business circles, politicians-as well as to foreign states, especially the Republic of China (Taiwan). These networks indicate that important sections of Japan's postwar establishment rallied behind anti-communism in the face of reforms that threatened their power at home and their vision for Japan in the world order after 1945. As a transwar history, this article adds to our understanding of Japan's transition from the age of empire to that of liberal democracy by qualifying narratives about the "progressive"nature of postwar Japanese politics. It argues that the vitality of anticommunism is symptomatic of the durability of particular political traditions, and reveals that, despite the significant reforms that Japan underwent after 1945, the Right was able to claim a space in the country's political culture that has been neglected by historians.