The present study aims to investigate Japanese language learners' motivation and their future Japanese self-images from the perspective of dialogical theory (Bakhtin, 1981, 1986). Bakhtin assumes that any use of language is dialogue between self and other, or mind and world, and that it is through the acquisition of speech genres of a language historically shared in society that various types of self emerge. Through the analysis of interview data obtained from two Japanese-as-a-second-language learners, the present study illustrates how their study of the language is motivated by their desire to engage in dialogue with others, present or imagined, who speak the language. By focusing on speech genres as mediation between self and other, it also shows how an individual future Japanese self-image is connected to the social practices of the Japanese-speaking community through the medium of the speech genres. Based on these findings, the present study argues that Bakhtin's concept of speech genres provides a framework for analyzing complex interactions between the individual learner's motivation, self and the socio-historical context, and thus, has the potential to expand the conceptual basis of language learning motivation studies.