Takaaki Ōishi is Aikoh Academy's third-year star athlete, dominating the boys' artistic gymnastics team with exceptional skill and widespread popularity. His drive stems from a troubled family life; his father vehemently opposes his gymnastics career, subjecting him to verbal abuse that fuels Ōishi's rebellious determination to succeed. This resolve leads him to recognize raw talent in novice rhythmic gymnast Hikari Kamijō, prompting him to volunteer as her trainer. Their mentorship blossoms into a close friendship, though Ōishi remains oblivious to Hikari's developing romantic feelings. Simultaneously, he becomes the object of affection for Hazuki Shiina, the school's top rhythmic gymnast, creating a love triangle that strains the girls' friendship and ignites a rivalry extending beyond the gym. Ōishi embodies the supportive and humble "Lovable Jock" archetype, offering unwavering encouragement for both Hikari and Hazuki's athletic dreams. His cheerful, approachable nature sharply contrasts with Mao Natsukawa's introversion, yet the two maintain an unexpected friendship despite both harboring feelings for Hikari.

Ōishi's character arc diverges between adaptations. The manga sees him reconcile his familial conflicts and continue his gymnastics career, eventually becoming engaged to Hazuki; the couple travels to Seoul to support Hikari at the 1988 Olympics. Conversely, the anime concludes by pairing him with Hikari, though this storyline remains underdeveloped due to the series' premature cancellation after 19 episodes; a brief flashforward depicts him recovering from an unspecified injury while aspiring to compete in the Olympics himself. Ōishi's narrative functions as a catalyst for the central romantic and competitive dynamics, his choices directly shaping the protagonists' emotional paths. His background as a victim of domestic conflict adds complexity to his otherwise optimistic persona, though this subplot is exclusive to the anime.