Koko Tsukishima is a student at Kazemi affiliated junior high, enrolled in class three three. She is introduced as a childhood friend of Yoshiyuki Sakurai and Nanaka Shirakawa. She has orange hair and blue eyes, and she is the same age as her classmates. Her early life shows a girl who was easily moved to tears and often felt insecure. Yoshiyuki played a significant role in helping her learn to smile, and she developed a forgiving disposition, once ending a childhood argument with him after he apologized. In the first season of the story, she gathers the courage to confess her romantic feelings for Yoshiyuki, and they begin dating. However, she eventually breaks up with him because she feels neglected when he spends excessive time with another girl, Minatsu, leading to renewed feelings of loneliness and insecurity. Her shyness and tendency to be teased by her friends Akane Hanasaki and Anzu Yukimura, who often joke about her romantic feelings, further illustrate her vulnerable nature. By the second season, she is shown to have grown into a more confident person, yet traces of her earlier fragility remain, as demonstrated by an instance in which she falls ill before a puppet show where she was to play a female lead. She is a member of the music club with her childhood friends. Her main motivation throughout is her affection for Yoshiyuki, but her personal journey also concerns her struggle with self‑worth and her desire to be treated as an equal in the relationship. She does not possess any supernatural or extraordinary abilities; her role is grounded in everyday school life and the emotional dynamics of the group. Her relationships with Yoshiyuki, Nanaka, and her other friends form the core of her interactions, and her growth is measured by her gradual move away from complete dependence on Yoshiyuki toward a more independent and assured state.