Kayo has brown hair in a bob haircut and brown eyes. She is often seen wearing a red kimono and carries pink bag.
She praise her older brother to complain about him afterwards. It seems she is a harsh person, but she is caring at heart. She often visit her brother, because he is rarely seen at home. She quickly become friends to Naoko Satomi and she visits her frequently. She likes to call people by her pet name. She calls her brother Nini (二兄)) and Naoko with Haru (春)).
She is the younger sister of Jiro. Happy and fun, Kayo first appears when Jiro returns home from school wanting him to play in the backyard. Jiro declines, however, and retreats to his room. Kayo is next seen bothering him in his room bugging him, then joining him to stargaze out on the roof that night. After Jiro leaves for the Royal University of Tokyo, Kayo begins to pursue a career in medicine wanting to become a doctor.
Kayo also appears at least twice throughout the rest of the film always impatient towards Jiro and his actions for being tardy and forgetful. However, Kayo also warns Jiro of Naoko's incurable condition of tuberculosis and loves her like a sister and witnesses Naoko's departure before her last goodbye.