Sustainable fashion has mainly been studied through analysis of consumers’ behavior trends, as well as brands’ business strategies, focusing mostly on Western case studies. Through the application of the Corporate Social Opportunity framework (Moon, 2012), this study aims to investigate how sustainable fashion brands in South Korea and Japan can gain competitive advantage while targeting environmental issues through social activities and profit from them. The results showed that the enhanced social and environmental activities can improve the brands’ sustainable performance, profits, engagement with society, as well as lead to competitive cost advantage in the market. The study offers a solution to the issue of generating profit and achieving competitive advantage by engaging in social and environmental activities. Furthermore, its attempt of filling the gap in the literature, related to sustainable fashion in the Asian region, highlights its significance.