The economic recession and changes in purchasing habits of young adults (aged 18–25) has led to a decline in the sales of Japanese fashion apparel. This younger generation’s choice of fashion items is primarily based on price. They are not devoted to a favourite brand with a frequent purchase history. Thus, developing customer loyalty and strengthening brand value are essential for the fashion industry. This study explores the improvement in fashion companies’ financial performance (FP) through young generation’s behavioural brand loyalty (BBL) from two aspects: social media brand engagement (BE) and loyalty programmes (LPs). This study listed 14 popular Japanese fashion brands which belonged to 14 publicly traded companies in Japan. Further, we surveyed 183 consumers about their brand related behaviours. The findings reveal the positive and negative effects of the same variable (BE and LPs) on the outcome (short- and long-term FP), indicating that not all activities related to BE and LPs boost FP. FP is influenced by various combinations of these causal factors and complex situations, such as consumers’ demographics and shopping characteristics. The results deepen our understanding of brand loyalty formation and the linkage among BE, LPs, and FP in a realistic marketplace, and offer multiple practical solutions to achieve high levels of short- and long-term FP by targeting the right consumers based on their specific characteristics.