"Uma Musume: Pretty Derby - BNW no Chikai" is a special anime series that serves as a prequel to the second season of "Uma Musume: Pretty Derby." The story centers on the rivalry and friendship between three horse girls: Narita Top Road, Symboli Rudolf, and Tamamo Cross, who form the group known as BNW (Best Nature Watch). Set in the world of horse girls—anthropomorphic characters inspired by real-life racehorses—the series explores their journey to become top athletes in the competitive world of racing.

The narrative begins with Narita Top Road, a talented but inexperienced horse girl, enrolling at Tracen Academy to pursue her dream of becoming a champion. She quickly encounters Symboli Rudolf, a prodigious and confident racer with a reputation for dominance, and Tamamo Cross, a determined and hardworking horse girl who idolizes Rudolf. Despite their contrasting personalities and approaches to racing, the three form a bond, driven by their shared ambition to reach the pinnacle of the sport.

As the story progresses, the series delves into the challenges they face, both individually and as a team. Narita Top Road struggles to find her footing and prove herself against more experienced competitors. Symboli Rudolf grapples with the pressure of maintaining her status as the undisputed best, while Tamamo Cross works tirelessly to close the gap between herself and her idol. Their dynamic is marked by moments of rivalry, mutual respect, and personal growth, as they push each other to improve and overcome obstacles.

The series also highlights key races and training arcs, showcasing the intense preparation and determination required to succeed in the competitive racing world. Through these events, the characters' relationships deepen, and their individual strengths and weaknesses are revealed. The narrative emphasizes themes of perseverance, teamwork, and the pursuit of excellence, as BNW strives to leave a lasting legacy in the sport.

"Uma Musume: Pretty Derby - BNW no Chikai" provides a detailed and engaging backstory for the BNW trio, setting the stage for their roles in the broader "Uma Musume" universe. The series balances character development with the excitement of racing, offering a compelling look at the dedication and passion required to achieve greatness in a highly competitive field.