In an increasingly competitive environment, it is very difficult for a company to secure sustainable competitive advantages with limited resources. In particular, the domestic sports fashion industry is at risk of survival due to the aggressive marketing strategies of global brands. In order to win the competition against those global leading brands, qualitative growth of the industry is essential, and it is also crucial to conduct research on diverse dimensions of the brand and build strategic alliances with other brands instead of simply developing new products with new materials. In particular, a co-brand strategy expected to create synergies through alliances with partner brands will have a positive effect on all companies participating in the alliance. As a result of examining brands through prior research on co-branding strategy, it can be seen that combining brands has an important influence on the success of co-branding. When reviewing the existing studies, we can find many articles on product suitability or brand fit, but few research on brand personality. For a brand, personality is defined as how consumers express themselves through a brand, and a unique brand personality can help consumers build a clear association with the brand. In particular, in brand marketing, it is very important to understand consumer characteristics because brand attitudes respond differently according to consumer characteristics. This study selected millennial consumers as major respondents because they are very familiar with various electronic devices and show strong consumption desire with sports fashion brands. The empirical analysis results are as follows. First, the co-brand personality fit between the target brand and the partner brand has a positive effect on brand trust and brand attachment. Second, the interaction effect between fashion involvement, a moderator used in the study to represent consumer characteristics, and co-brand personality fit on brand attachment is demonstrated. Third, through empirical analysis, it is proved that the interaction effect between the co-brand personality fit and fashion involvement on brand attachment is mediated by brand trust.