In a world increasingly driven by both technological advancement and ecological sustainability, understanding how cultural values such as mottainai influence green entrepreneurship is essential in fostering sustainable business practices and addressing resource inefficiencies. This research project investigates the influence of mottainai—a principle embodying a profound sense of regret over waste—on Japan’s green entrepreneurship. Although well-documented in consumer behavior and organizational sustainable practices, its impact on the entrepreneurs who develop and commercialize green technologies remains underexplored. This study sheds some light on this gap by examining how mottainai influences anentrepreneur’s foundational values and business strategies. Employing a qualitative methodology, this investigation relies on semi-structured interviews with one green entrepreneur based in Japan, focusing on how he interprets and integrates mottainai into his operations. Through thematic analysis of the interviews and secondary data, the study provides new insights into how mottainai, a traditional cultural value, can be harmoniously integrated with modern entrepreneurial practices to jointly enhance environmental and economic sustainability globally.