Reina Gojō is Yuma Gojō's younger sister and holds the position of student council president at Odachi High School, having won the title "Miss Oodachi High" twice. She initially bears deep resentment toward Hinomaru Ushio after his duel victory over her brother, refusing to accept Yuma's defeat. This animosity grows when she sees Yuma in a mawashi for the first time, finding it embarrassing. Despite objecting to Yuma joining the sumo club, she eventually becomes one of its managers to support him, leveraging her student council role to secure increased funding.

Initially dismissive of sumo, Reina knows nothing about the sport and mocks it. However, closely observing matches and feeling the impact of collisions and the technical complexity of maneuvers firsthand begins to shift her view toward appreciation of its aesthetics. A turning point comes during Hinomaru's match against Sōsuke Kuze, where she acknowledges her growing understanding and thanks fellow manager Chizuko Hori for her guidance. Through repeated exposure, Reina recognizes Hinomaru's resilience and skill, particularly how he captivates audiences by rising after each setback, leading her to develop a deep admiration for his sumo style.

Reina's character arc illustrates a journey from ignorance and prejudice toward sumo to a nuanced respect for its athleticism and cultural significance, driven by her commitment to her brother and her evolving perspective as a club manager.