Tazuna Hayakawa serves as secretary to the principal at Tracen Academy, overseeing administrative duties to ensure a functional environment for students and staff. She consistently presents a calm, gentle demeanor, offering guidance to newcomers while strictly enforcing rules like apprehending curfew violators with notable speed. Her distinctive appearance features a green uniform, matching hat, and yellow necktie. Her dark brown hair is styled short in the front and long in the back, tied with a yellow bow; she stands 166 cm tall. A recurring mystery implies her potential identity as an Umamusume, supported by extraordinary physical feats. She demonstrates the ability to outrun elite horse girls like Taiki Shuttle and Special Week, accelerating instantly from a standstill while carrying documents or in awkward postures. She always conceals her ears under her hat, with official discarded designs suggesting horse ears, fueling speculation. Strong evidence links her to the legendary racehorse Tokino Minoru, who retired undefeated after 10 races but died young in 1951. Shared connections include identical birthdays (May 2), her surname Hayakawa (combining "excellent horse" and "river"), her first name Tazuna (meaning "rein"), and outfit elements like 10 buttons symbolizing Tokino Minoru's victories. Her watch worn on the right wrist aligns with Tokino Minoru’s sand crack injury on the right front leg. She expresses fondness for movies, paralleling Tokino Minoru’s owner who operated a film company and produced "The Illusionary Horse" as a tribute, and exhibits acute concern about injury prevention and medical equipment delays, reflecting Tokino Minoru’s fatal leg condition. Her personal interests include cooking rice in a clay pot during celebrations and consuming carrots, ramen, and gyoza. She maintains a close, casual friendship with Maruzensky, sharing drinks and conversations outside work, contrasting her typically formal interactions. Other characters, including Symboli Rudolf and the first Triple Crown winner St. Lite, treat her with familiarity and trust. She appears consistently across anime seasons: In Season 1, Episode 1, guiding Special Week after a late arrival and later delivering urgent news; in Season 2, greeting students and announcing achievements; in Season 3, welcoming newcomers. Spin-offs like "Umayon" (episode 11) and "Umayuru" (episodes 11–12) show her mediating conflicts and displaying subtle anger when property is damaged. Within the game, she functions as a navigator providing training advice, race predictions, and post-loss analyses. Her Support Cards (R and SSR variants) reduce stamina loss during training, boost motivation, and offer unique skills. Declining her "outing" invitations yields stamina skills but forfeits beneficial events. Players colloquially dub her the "green devil" due to her teasing appearances in gacha animations.