Using the epistemic stance concept (Heritage 2013) and conversation analysis, this study examines L2 language learner identity evolution from a longitudinal socio-interactional viewpoint and proposes a different perspective in exploring L2 evolution. English as a lingua-franca communication at a university dormitory in Japan was gathered during 22 months between two participants with diverse L1s. This study indicates social epistemics and identity as a framework for investigating (L2) language learner growth.