The rapid adoption of Generative Artificial Intelligence (GenAI) has transformed digital marketing by enabling brands to produce, personalize, and distribute content at unprecedented scale. However, increasing dependence on AI-generated content may create communication homogenization and weaken perceived brand authenticity, making differentiation and meaningful consumer engagement increasingly challenging. This study examines how authentic brand storytelling and GenAI can be strategically leveraged to strengthen brand differentiation and enhance consumer engagement within the digital marketing ecosystem. Using a library research approach, the study analyzes relevant books, peer-reviewed journal articles, scientific reports, and previous studies through content analysis. The findings indicate that authentic brand storytelling provides distinctive narrative meaning, while GenAI functions as an enabling capability for scalable, personalized, and multimodal communication. Brand differentiation emerges as a strategic mechanism connecting these resources with cognitive, emotional, and behavioral consumer engagement. The study concludes that GenAI creates greater strategic value when governed by authentic brand identity, human oversight, narrative consistency, and consumer participation rather than used merely to increase content volume.