The sociocultural perspective of second language teacher education (L2TE) (e.g., Johnson, 2009), unlike the traditional one, values the importance of teacher development through actual teaching practice. Student teachers' (STs) initial beliefs should be challenged and reconstructed by taking into account particular teaching contexts. This study investigated the advantages of conducting online activities with L2 learners in L2TE. Using the genetic (Vygotsky, 1981) and activity theory (Leontiev, 1981) frameworks, this study addressed the following questions: (1) What contradictions emerge during online activities? and (2) How do the contradictions relate to STs' identity development? STs in a Japanese language education program engaged in three wiki activities with learners from Japanese language classes abroad. Data were collected in the domains of the genetic framework and included the STs' autobiographical statements, journals, final reflections, on-site peer dialogue, and observation notes. Contradictions between and within elements (Engeström, 1987) were identified and triangulated across the data sets. The data illustrated that the STs who initially relied on their native speaker authority gradually realized the socially and culturally complex roles required for L2 teachers. These findings suggest that online activities in L2TE provide opportunities for not only media literacy but also professional identity development.