Kayo Touyama is a central supporting character known for being the best friend of the protagonist, Mugi Asai. She has been a close companion to Mugi since their junior high school years, making her one of the few people with whom Mugi can converse almost normally without severe stuttering or losing her voice. Her personality stands in stark contrast to Mugi's extreme shyness; Kayo is an outgoing, self-assured, and sociable girl who has no trouble approaching others. In fact, it was Kayo who first reached out to the isolated Mugi, deciding to keep her company and thereby forging a deep and lasting friendship.

Kayo’s primary motivation is her passion for photography. This is not merely a casual hobby but a deep-seated dream she hopes to turn into a career. She is rarely seen without her beloved camera, which she uses to capture everything around her. Her ultimate goal is to work as a professional photographer, even though she privately doubts whether her talent is sufficient for such a path. This ambition is a significant driver of her actions throughout the story.

In the narrative, Kayo plays the vital role of Mugi's steadfast anchor and biggest cheerleader. She is one of the main reasons Mugi gains the courage to join the Drama Research Club after being persuaded by Nono. Kayo consistently encourages Mugi to have more confidence in herself and tries to provide motivation during the club's practice sessions. Her support is not just verbal; she and fellow student Chitose become regular audience members at the club's meetings. Kayo meticulously documents every detail of Mugi's journey and growth with her camera, capturing moments that are both significant and mundane. As she witnesses her friend slowly but surely develop, gain confidence, and find new friends within the club, Kayo feels overjoyed, and this experience reinforces her own determination to pursue her dream of becoming a photographer.

Regarding her relationships, the bond with Mugi is the most significant. Kayo is arguably the one person who understands Mugi's struggles intimately and is dedicated to helping her overcome them. Her own personality, being the opposite of Mugi's, complements their friendship perfectly, as she can easily do the social heavy lifting that terrifies her friend. She is also a member of the Photography Club at Kumataka High School, having known since the start of the school year that she would join, as it aligns perfectly with her greatest passion.

Kayo undergoes a subtle but clear development. Initially, she is a supportive observer, using her camera to document the lives of others. Over time, her role shifts as she finds personal validation in Mugi's success. Seeing her friend change for the better strengthens Kayo's own self-belief, pushing her to actively work toward making her own dream of working as a photographer a reality. This culminates in a significant life decision after her first year of high school, as she leaves Japan to study photography overseas, an action that demonstrates her commitment to following her own path.

Kayo’s most notable ability is her skill and keen eye for photography. She is deeply passionate about framing and capturing moments, and her work consistently impresses those who see it, particularly Mugi, who is always delighted by her friend's photographs even though she is shy about being a subject herself. Her equipment, a camera she keeps with her at all times, serves as an extension of her observant and supportive nature. Physically, she is depicted with blue eyes and green hair cut to neck-length.