This study demonstrates the ways in which discourses in a state-sponsored volunteer program incited transformations of individual subjectivities, focusing on a group of Japanese language teacher volunteers training in Japan to become teachers of Japanese as a heritage language for the country's diaspora (Nikkei) population in South America. As teachers of heritage Japanese at Japanese language schools in these Nikkei communities, their work was central to Japan's diaspora strategies, which reframe the Nikkei population as Japan's "diplomatic assets" connected to Japan through their Nikkei identity. Focusing on these language teachers as important actors in Japan's diaspora strategies, this study illustrates how their encounter with the institutional discourses resulted in the transformations of their subjectivities. Such transformations occurred during the volunteer training sessions hosted by Japan's international cooperation agency to conceptualize their roles as teachers of Japanese as someone's heritage language. By illustrating the ways in which these volunteer individuals' transformations fit within state diaspora strategies, this article underscores the role of state actors in the process of subjectification, which has tended to be overlooked in previous studies of governmentality.