Kyōko Kōda is the eldest daughter of the Kōda family and the biological older sister of Ayumu Kōda. She becomes the adoptive sister of Rei Kiriyama when Rei is taken into the Kōda household after losing his own family in a traffic accident. She is four years older than Rei. A beautiful young woman with bra‑length blonde hair and blue eyes, she is often seen dressed in light‑colored clothing.

Kyōko’s early life was defined by her father Masachika Kōda, a professional shogi player who measured his children largely by their shogi ability. Kyōko herself was a promising player, reaching the level of shodan (first dan) in middle school, and she harbored a strong ambition to become a professional shogi player. However, when Rei, who possessed extraordinary natural talent, joined the family, her father judged that Kyōko could not beat Rei and forced her to give up shogi. This experience left a deep wound: she felt that her existence had been denied and that she had been replaced by an outsider.

As a result, Kyōko displays a fierce, hot‑tempered personality and holds a deep grudge against Rei. She frequently directs caustic words and even physical violence toward him, attempting to lead him into failure or emotional distress. Beneath her aggressive exterior lies a craving for love and validation, particularly from her father, whom she feels never gave her enough attention. She has a proud and self‑centered manner, but she is also vulnerable and lonely, though she rarely shows this side. Her anger at Rei is intertwined with a twisted form of care; the two share a common history of feeling unloved within the same family, and they remain bound together even as they hurt each other.

Kyōko’s motivations are largely driven by her unfulfilled need for affection and recognition. She becomes involved in a complicated, destructive relationship with the older married shogi player Gotō Masamune, seemingly as a way to feel wanted. Through this relationship, she eventually witnesses Gotō’s devoted visits to his terminally ill wife, which forces her to confront the depth of his loyalty. This experience helps her begin to understand Rei’s feelings of loneliness after losing his family, and she gradually starts to soften. Over the course of the story, she reflects on her past actions and quietly wishes for Rei’s happiness, marking a subtle but meaningful development in her character.

In the narrative, Kyōko functions as a recurring source of tension and a dark mirror for Rei. She represents the trauma and guilt that Rei carries about having disrupted the Kōda family. Her role is not that of a simple villain; she is a deeply wounded person whose actions are rooted in real pain and neglect. Her key relationships include her fraught bond with Rei, her dependence on Gotō, her strained connection with her father, and her somewhat distant relationship with her younger brother Ayumu, who also withdrew from shogi after being overshadowed by Rei.

Kyōko is notable for her shogi ability—an aggressive, forceful style that once made her a strong middle‑school player—and her sharp perceptiveness, which she sometimes uses to manipulate others. Despite her abrasive behavior, she undergoes growth as she begins to recognize the pain of those around her, including Rei, and slowly moves toward a more empathetic understanding.