<p>Community-engaged learning (CEL) has gained attention in health professions education, yet there remains limited explanatory understanding of how it generates learning processes in East Asian contexts characterized by hierarchical professional cultures. This study used realist evaluation to examine a two-week rural community diagnosis practicum involving Japanese medical, nursing, and pharmacy students. Data were collected through ethnographic fieldwork, students’ written reflective reports, and ten focus group interviews conducted in 2023 and 2024. Analysis identified five key context–mechanism–outcome (CMO) configurations explaining how learning unfolded under specific conditions. These included disruption of perceived “correctness” through lived community encounters, reframing deficit-oriented assumptions about resources through community storytelling, adaptive learning across institutional boundaries, reconsideration of urban-centric career values, and dialogic engagement enabled by students’ non-expert and outsider positioning. Across configurations, learning was generated when contextual conditions disrupted certainty and loosened institutional scripts, activating mechanisms of reflexive reappraisal, adaptive sense-making, and relational openness. These mechanisms contributed to outcomes such as increased epistemic humility, reorientation of professional assumptions, and heightened sensitivity to relational and contextual dimensions of care. Importantly, the uncertainty and ambiguity inherent in CEL functioned not as limitations but as conditions that enabled these learning processes to occur. By specifying how, why, and under what conditions CEL operated in this setting, the study offers a mechanism-focused explanation of learning in hierarchical and collectivist contexts. Findings from rural Japan highlight the theoretical transferability of these explanations and provide guidance for the design and evaluation of CEL initiatives in other sociocultural settings.</p>