Moral education in Islamic boarding schools (pesantren) aims to cultivate sustainable Islamic character. However, the transition from the highly structured pesantren environment to post-graduation life often presents significant challenges for alums in maintaining moral values. This qualitative study explores the continuity of moral education among four pesantren alums aged 19–20 through a case study approach involving in-depth interviews and participatory observation. Data were analyzed using the Miles and Huberman model. The findings indicate that the interaction between internal factors, such as habitual practices, spiritual capacity, and self-confidence, and external factors, including social environment, peer influence, social media, and community support, shapes moral sustainability. The pesantren’s moral formation methods role modeling, habituation, advice, and narrative remain influential, though with varying degrees of intensity. This study also reveals that peer-based narratives and storytelling function as a crucial mechanism for moral reinforcement, as they foster emotional engagement and strengthen collective religious identity. Furthermore, the weakening of moral practice is more closely associated with the decline of supportive social structures than with individual moral commitment alone. Therefore, sustained mentoring and the strengthening of alum communities are essential to support the long-term continuity of moral character.