This study examines the structure and functions of the Raja Tuan customary governance system, the oversight role of the Maran Clan, and its potential to revitalize customary-based civil society in East Flores Regency. The study employed a single-case study design conducted in Ilepadung Village using a descriptive qualitative approach. Data were collected from 15 informants through participant observation, in-depth interviews, focus group discussions (FGDs), and document analysis, and were subsequently analyzed thematically using triangulation, member checking, and an audit trail. The findings indicate that, within the Raja Tuan system, customary-based civil society is context-specific and not necessarily horizontal or egalitarian. Instead, it operates through hierarchical-relational structures grounded in cultural legitimacy, in which the Maran Clan performs deliberative, mediating, and social oversight functions through cultural authority and collective moral control. Within the local context examined, the revitalization of the Maran Clan expands the institutional functions of customary governance by strengthening cultural legitimacy, social oversight, and accountability in village governance. This study contributes to the literature on deliberative democracy and civil society by demonstrating that, within the Global South, deliberation and accountability do not depend solely on formal institutions or horizontally structured civil society organizations, but may also develop through customary institutions grounded in cultural legitimacy.