Biwa Hayahide is a character from the short animation series Umayuru: Pretty Gray, where she appears as a central figure in one of the episodes. She is a student at Tracen Academy and a member of the Ritto dormitory. Her appearance is striking and distinctive, characterized by a long, incredibly voluminous mane of silver-white hair which she keeps free-flowing, adorned with golden clips near her horse ears. She has yellow eyes and wears a pair of red under-rim glasses, an accessory that references her real-life counterpart's racing blinkers. Her physique is tall and athletic, standing at 171cm.

Personality-wise, Hayahide is defined by her cool, calm, and highly logical nature. She is a theorist through and through, believing that victory can be systematically derived through meticulous analysis, calculation, and strategy. She breaks down every problem, including race tactics, into a formula and values the practical application of her theories, ensuring her methods are not just abstract ideas. Despite her outward image of being perfectly composed and intelligent, she possesses notable insecurities. She is extremely self-conscious about the size of her head and the volume of her hair, reacting defensively and disproportionately to any comment, no matter how innocent, that even remotely references a "big head" or "fluffy hair". This trait is a playful nod to the real racehorse Biwa Hayahide, who was known for having an unusually large head. While she can seem rigid and overly serious, she privately wishes she could be more flexible and less strict with herself.

In the context of Umayuru: Pretty Gray, Hayahide takes a leading role in the episode titled "Destiny's Tide—the Turbulent Relay". In this episode, she gathers Hishi Miracle and other fellow racers for a test run in preparation for the Spring Fan Fest. Her plan for the relay race is characteristically strategic, though it proves to be so unconventional that it bewilders her teammates, who become exasperated upon learning there is no official finish line to her course. This showcases her role as an initiator and a thinker who operates on her own unique wavelength.

Her key relationships are deeply rooted in the lore of the wider franchise. She is the older sister of Narita Brian, a relationship that is central to her character. While she constantly worries about her younger sister's health and diet, she has also honed her own formidable abilities in an effort to compete with Brian's overwhelming natural talent. She shares a close, friendly rivalry with her classmates Narita Taishin and Winning Ticket, with whom she forms the famous trio known as "BNW". Her roommate is the flamboyant T.M. Opera O, whose theatrical antics, such as scattering rose petals in their room, often try Hayahide's patience.

Regarding development, her journey is one of leveraging intellect to overcome the pressure of being compared to a prodigious sibling. Her logical approach to racing is a direct response to the need to find her own path to victory, distinct from relying on raw, innate ability. Her notable abilities are a blend of academic and athletic prowess. She excels in all academic subjects, particularly mathematics and the sciences. On the track, she is a powerful competitor in middle and long-distance races, with a particular affinity for using strategy to control the race from a forward position. In a more quirky and beloved demonstration of her skills, she is famously able to eat an entire banana in under five seconds, a feat she has been known to showcase in competitions.