In the present study, we examined changes in identity dynamics during adolescence using the Dimensions of Identity Development Scale (DIDS), focusing on social and cultural factors possibly affecting identity formation. Identity formation among adolescents outside Western countries is largely unexplored; therefore, we focused on adolescents in Japan. We conducted a longitudinal study with 4 annual measurement points examining 968 Japanese adolescents (49.7% females). Two cohorts of participants were 13 and 16 years old at Time 1 and were followed until 16 and 19 years old, respectively. Latent class growth analysis extracted 3 identity trajectories corresponding to those found in previous research (i.e., achievement, troubled diffusion, and carefree diffusion) and 2 transitional trajectories newly identified in the present study (i.e., troubled diffusion-to-moratorium and moratorium-to-achievement). Adolescents following the achievement trajectory showed the best subjective well-being, whereas troubled diffused adolescents showed the worst. Furthermore, early-to-middle adolescents and urban adolescents tended to follow a low-commitment trajectory, whereas middle-to-late adolescents and rural adolescents tended to follow a high-commitment trajectory. These findings suggest that identity development proceeds toward integration during adolescence, but simultaneously, diverse developmental trajectories exist and incorporate contextual factors. Thus, in Japan, adolescence may be a period of identity formation for some adolescents, but not for others.