This article aims to situate itself within religious anthropological scholarship through a comparative study of Indigenous religious transformation in Malaysia and Bangladesh. Methodologically, the research combines phenomenological interpretation with a decolonial perspective rooted in a relational ontology that sees human beings as embedded in networks of land, ancestry, and community. Drawing on ethnographic engagement, narrative accounts, and interpretive analysis, the study examines two Indigenous communities—the Orang Asli of Peninsular Malaysia, where conversion to Islam occurs, and the Santal of northern Bangladesh, where conversion to Christianity has been significant. The findings suggest that religious conversion in these contexts rarely results in a straightforward doctrinal change. Instead, it unfolds as a negotiated transformation of moral life, kinship relations, and social belonging within existing cultural worlds. Indigenous actors often reinterpret new religious teachings through their own cosmological frameworks, creating hybrid moral landscapes where elements of Indigenous relational knowledge coexist with new religious practices. To understand these dynamics, the article develops the Nas–Tadabbur–Ihsan model, connecting relational ontology (Nas), reflective epistemology (Tadabbur), and ethical practice (Ihsan). While these concepts originate from Islamic ethical vocabulary, the framework functions as a universal analytical tool, emphasizing shared human capacities for reflection, relationality, and ethical responsibility. Therefore, the study suggests that Indigenous conversion is best understood as an ongoing process of ethical negotiation and relational reconfiguration rather than a mere cultural rupture or assimilation.