Kyoko is introduced as the leader of a female delinquent group known as the Tornado Gang, and she is depicted as a beautiful young woman with blonde hair and long eyelashes. Her initial appearance in the story places her in stark opposition to the world of professional baseball and its dedicated athletes. She first encounters the pitcher Hyuma Hoshi and his rival Hosaku Samon at a movie theater, where she and her gang attempt to provoke and blackmail Samon by falsely accusing him of being a pervert. When Kyoko dismisses professional baseball as fixed, Hyuma reacts with anger and slaps her, an incident that paradoxically causes her to develop feelings for him, creating an unusual love triangle as Samon simultaneously falls in love with her.

Her motivations shift dramatically over the course of the narrative, moving from self-serving delinquency to genuine care for others. A pivotal moment occurs when Hyuma, in despair, attempts to stab his own pitching hand. Kyoko intervenes to protect him, and during a subsequent altercation with a yakuza boss, the nerve in her pinky finger is severed, leaving it permanently immobilized. This injury represents her first major sacrifice for another person, and it serves as a turning point in her character arc. After being hospitalized, she reverts to her old ways by throwing a wild party and attempting to blackmail the hospital, which forces Hyuma to realize they live in completely different worlds. He offers her his apartment and financial assets as compensation and leaves her. However, when Hyuma later returns with Samon to find his home ransacked, he instead discovers the apartment untouched and a letter from Kyoko left in the door. In this letter, she reveals her true feelings and urges him to return to baseball, a plea that shocks Hyuma and strengthens his determination to reclaim his career as a player.

Kyoko's key relationships are central to the story. Her connection with Hyuma is complex, born from conflict and evolving into mutual respect and inspiration. It is while watching Kyoko attempt to throw an apple to Samon on a train using her injured hand that Hyuma gains a crucial hint for developing his most powerful pitch, the Major League Ball No. 3. Her relationship with Samon develops alongside her own growth. As Samon suffers in silence over his love for Kyoko, Hyuma eventually advises him to confess, recognizing the inner beauty she has demonstrated through her sacrifice. Kyoko ultimately accepts Samon's proposal and marries him.

Kyoko undergoes a significant transformation by the end of her story. Her rough and abusive manner of speech disappears entirely, and she adopts the polite language of a refined young lady. Furthermore, her formerly blonde hair has turned black, visually symbolizing her complete departure from her past as a gang leader. In the sequel, New Star of the Giants, she is shown living a happy domestic life with Samon and his younger siblings, and when asked if she still likes Hyuma, she responds with a smile that she likes him as much as her husband does, indicating a comfortable and settled existence. While she does not possess athletic abilities like the baseball players, her injured finger and the simple act of throwing an apple prove to be an unexpected catalyst for one of the series' most important baseball techniques. Her role in the story is that of a catalyst for change, first as an antagonist, then as a source of inspiration and a figure who, through personal sacrifice and growth, finds a place away from the baseball field that is nonetheless tied to its emotional core.