Movie
Description
Kayo Horikoshi is the younger sister of Jiro Horikoshi, the protagonist of the story. She is a fictional character created for the film, as the historical Jiro Horikoshi did not have a sister. Kayo is depicted from childhood into adulthood, with brown hair styled in a bob haircut and brown eyes. She is frequently seen wearing a red kimono and carrying a small pink bag.

In personality, Kayo comes across as harsh and impatient, often criticizing her brother for being tardy or forgetful, but this exterior masks a deeply caring and loving heart. She is a happy and fun-loving individual who is not afraid to speak her mind. Despite her critical nature, she is fiercely loyal to her family and quickly forms a close, sisterly bond with Naoko Satomi, Jiro's wife. She expresses her affection through unique pet names, calling her brother Nini and Naoko Haru.

Kayo's primary motivation is her love for her family and her desire to see them well. She pursues a career in medicine, becoming a doctor, which likely stems from a practical understanding of life's fragility. Her role in the story is that of a supportive yet grounding presence for Jiro. She acts as a bridge between his personal and professional life, often being the one to deliver difficult news or provide a dose of reality. She warns Jiro about Naoko's incurable tuberculosis, demonstrating her protective nature and her wish to prepare him for the heartache to come.

Her most significant relationship is with her brother, Jiro. She is often seen visiting him because he is rarely at home, and she serves as a connection to his past and his family. She also develops a crucial relationship with Naoko, whom she loves like a sister; she frequently visits Naoko and is present for her final departure. Over the course of the story, Kayo develops from a child pestering her older brother to play in the backyard into a mature medical professional. She witnesses the major events of Jiro's life, including his marriage and the tragedy of his wife's illness, evolving from a playful sibling to an anchor of emotional support and practical wisdom. While she possesses no fantastical abilities, her notable skill is her medical knowledge as a doctor and her perceptiveness regarding Naoko's declining health, which proves to be a critical element in the narrative.