Recent approaches to the study of Euro-American empires have increasingly highlighted the importance of what the anthropologist and historian Ann Stoler calls “cultural sensibilities” (rather than skin color) as the de facto criterion by which national membership was assigned. Such critical interventions have succeeded in calling into question the seeming immutability of “black-and-white” racial distinctions, which most scholars have conventionally understood as the most important justificatory and operational logic of colonial rule. However, when viewed from a historical perspective anchored in (East) Asia, these debates have curiously failed to consider the case of Japanese colonialism, where deeper physiognomic similarities between colonizer and colonized made it even more important to create, mark, and patrol the shifting boundaries between the diverse members of the multiethnic national community. As a way of dialoguing with and thereby enriching Euro-centric debates on the place of racialized culture in the study of empire, this paper will show how attention to colonial sensibilities figured centrally in the government-general’s avowed goal to “assimilate” colonized Koreans into the larger emperor-centered community. However, as I will argue, this elusive project of cultural incorporation revolved around mutually constitutive definitions of Japanese-ness and Korean-ness that the colonial state was seriously invested in managing but, in practice, could hardly control. On the one hand, essentialized discourses of Korean-ness as commonly expressed by the racialized epithet yobo demonstrate how Japanese settlers aimed to distance themselves from native inhabitants and thereby justify their privileges over them. While challenging the homogenizing initiatives of the colonial state, these discourses also helped to create equally idealized notions of Japanese-ness, sensibilities the government-general could appropriate to measure the degree to which Koreans had been incorporated into the imperial community. On the other hand, inevitable encounters between Japanese settlers and the local population — elaborate efforts to insulate themselves from the “contaminating” sensibilities of Koreans notwithstanding — also produced anxious debates on the so-called yobo-ization of Japanese settlers. Charges of having embodied attributes of Korean others not only suggests that some settlers had failed to become sufficiently “Japanese,” but also underscores how the project of colonial assimilation relied upon a multidirectional flow of practical sensibilities which often transversed and transgressed the carefully constructed, discursive boundaries of ethnicity.