We trace the shift from a nascent to a mature policy subsystem by examining a hitherto overlooked aspect in policy process scholarship: the relationship between advocacy coalition beliefs and the narratives they express over time. The empirical focus of this case study is Sweden's Preventing and Countering Violent Extremism (P/CVE) policies between 2013 and 2022. We utilize aspects of the Advocacy Coalition Framework and the Narrative Policy Framework to examine narrative polarization, coalition density, and agreement in character expression. The findings show two coalitions based on policy core beliefs across three distinct time periods that coincide with the policy subsystem shifting from a nascent to a mature level of development. Furthermore, in the Swedish P/CVE context, the evolution to a mature subsystem coincided with the hardening of coalitions that became more polarized in their narratives with greater division in their character expressions. We conclude with a call for theoretical attention to subsystem development.