This article examines the predicament of Manchukuo’s “Concordia of Nationalities” doctrine as it was practiced. Japanese ethnology/folklore studies were initially intended to develop an understanding of the Japanese nation itself and to cast off the dominant Western perspective for interpreting other cultures, but with Japanese imperial expansion and the acquisition of colonies, ethnology and folklore studies began to change. Faced with Manchukuo’s diverse ethnic composition, Japanese colonial officials coined the slogan of a “Concordia of Nationalities” in hopes of diluting Han Chinese historical and cultural influence. Ethnology/folklore studies then became a tool for putting this doctrine into practice. In the various Japanese surveys of old myths and legends, of which investigations into the Oroqen are the most representative, Manchuria is shown to be non-Han in nature, with efforts made to draw links to Japan. Despite this, the Japanese in Manchuria changed their views on the “Concordia of Nationalities” and began reflecting on the validity of colonial policy. This study reveals a divergent sense of nationality between Manchukuo and Japan, as seen in the experiences of Omachi Tokuzo and Fujiyama Kazuo, as well as in the literary works of other Japanese in Manchuria. In short, despite initial intentions, these types of folklore studies and the “Concordia of Nationalities” formed a double-edged sword that exposed the predicament of the empire’s mythos of a unitary nation and also prompted Japan to take up “regionalism” and other ideologies in an effort to recalibrate its aggressive and expansionist activities.