The article explores the interpretation of sustainability from the Japanese perspective. Drawing from four case studies, the article asks: how is sustainability interpreted in the context of urban regeneration in Japan? Two case studies (Musashi Kosugi and Kashiwanoha) are high-rise, high-density developments that use new building technology but have little or no attention to the context. UR Yokodai danchi renovation and Kamakura ‘regional capitalism’ are community-led projects that preserve the existing buildings and the local community. These four developments are analysed in relation to sustainability criteria that includes socioeconomic targets and conservation of the townscape. The findings suggest that although Musashi Kosugi and Kashiwanoha are prime examples of urban densification and the use of smart technology, challenges posed by the post-population peak society, oversupply of housing, and consequences of the pandemic question the flexibility and sustainability of these developments. Yokodai danchi demonstrates the potential of postwar housing stock to accommodate sustainable renovation and provide affordable housing. Kamakura ‘regional capitalism’, rooted in joint venture between the local governance, entrepreneurs, and old residents, middle-density and mixed-use urban fabric, can develop into flexible, idiosyncratic, and family-friendly environments. The research suggests that the Japanese government’s new policies such as Super Cities Program should not restrict the vision of sustainable cities to new build developments and that urban densification should not always be taken as a synonym to sustainable city developments.