This study aimed to examine the relations between educational and interpersonal identity trajectories and psychosocial functioning based on a three-factor identity process model. A total of 968 Japanese adolescents including 13- and 16-years-olds (49.7% female) participated in a four-wave longitudinal study. Latent class growth analysis extracted five identity trajectories in each educational and interpersonal identity domain and revealed (a) high prevalence of low commitment identity trajectories, (b) absence of the closure trajectory, and (c) changeable identity trajectories that have not been identified in Western context (i.e., the Netherlands). Furthermore, a latent change model revealed dynamic relations between identity trajectories and psychosocial functioning. These findings provide critical insights into the diverse and dynamic pathways of identity formation during adolescence in Japan.