This book presents a rigorous, historically grounded analysis of the mechanisms that sustain brand formation, successor development, and transgenerational entrepreneurship in Japanese long-established family firms. Through an in-depth, multi-method case study of YAMAMOTO-NORITEN—a seven-generation, 175-year-old seaweed company in Nihonbashi—it fills a major gap in family business research, where longitudinal, empirically documented studies of individual firms remain rare. The book contributes three major scholarly advancements. First, it offers a detailed account of how legacy brands emerge as accumulations of intangible assets, socio-emotional wealth, symbolic capital, and embedded family narratives. Second, it advances the concept of successor legitimacy by integrating Weberian traditional authority, Linton’s status theory, and contemporary legitimacy research, arguing that successors must navigate a “constraint–autonomy dilemma.” Third, it proposes a model of the legacy accumulative chain, demonstrating how innovations and inherited resources interact across generations in a long-term, path-dependent process. The work targets practitioners, scholars, and graduate students in family business, entrepreneurship, Japanese management, organizational theory, and socio-economic history. It provides a robust empirical foundation through company documents, genealogies, and extensive oral histories, illustrating how intangible assets and institutional embeddedness shape continuity and competitive advantage. Overall, the book offers a theoretically innovative and empirically rich contribution to global family business scholarship.