Today, it is customary to describe the Japanese archipelago in terms of the neutral distinction between the Sea of Japan side (Nihonkai-gawa) and the Pacific Ocean side (Taiheiyō-gawa). For much of the 20th century, however, these regions were called respectively ura Nihon and omote Nihon, or roughly “the Backside of Japan” and “the Frontside of Japan.” This continued until the 1960s when the terms were criticized as discriminatory and their usage terminated. How, then, did the Sea of Japan coastal region come to be known by the discriminatory term “the Backside”? Intrigued by this question, this paper retraces the little-studied history of the place name ura Nihon. As I will show, behind the place name ura Nihon are forgotten histories not just of uneven domestic economic development but also colonial expansion and empire building in Northeast Asia. That is, ura Nihon is both a history of the Japanese nation and of the empire. By retelling this history, the paper seeks to contribute to understanding the ways in which empire building in Northeast Asia was connected to the domestic history of the Japanese nation-state in the 20th century.