Kiyori Torioi is a supporting character in the series who serves as a close friend and classmate to the protagonists, Sumika Murasame and Ushio Kazama. She is a constant presence in their social circle, frequently seen with them during lunch breaks and on various outings. Her role within the group is often that of a grounded and pragmatic observer, providing a contrast to the more emotionally tumultuous dynamics between her friends. Kiyori is a member of the school's music club, specifically the brass section, an activity that occupies a significant portion of her time outside of class.

Kiyori is most easily recognized by her cheerful and easygoing personality, as well as her constant snacking. She has a playful demeanor and a notable fondness for food, with her peaceful lunchtime being something she values greatly. Despite her generally supportive and friendly nature, she is not afraid to be blunt. She often becomes exasperated with Ushio's habit of developing fleeting crushes and constantly talking about wanting a cute girlfriend, a reaction she shares with most others. A signature phrase of hers is to dramatically declare, "I kindly decline!" followed by a fake laugh, often used to avoid emotional situations she finds tedious.

One of Kiyori's key functions in the story is to act as a supportive, straight friend who is entirely accepting of her friends' sexualities. While she is not interested in girls herself, she is well accustomed to Ushio being a lesbian and shows no signs of prejudice. Her early characterization includes moments of ignorance, such as expressing confusion about how a lesbian could attend a co-ed school, but she quickly evolves into one of the most supportive characters in the series. She is perceptive, seemingly aware that Sumika's feelings for Ushio are more than platonic, and on occasion, she attempts to give the two of them time alone, although she is generally more concerned with having a good time than with unnecessary emotional drama. This supportive role extends to the formation of the Girls' Club; despite not officially joining because she is unsure of its "suspicious activities," she remains with the group because she thinks it might be fun.

Kiyori's key relationships are primarily with Sumika and Ushio. She is their best school friend, and the three form a tight-knit trio. Her friendship with Ushio is characterized by her good-natured exasperation with Ushio's love life, although she remains a caring and loyal friend. With Sumika, she shares a quieter camaraderie, and she seems to understand Sumika's hidden feelings without needing them to be explicitly stated. Kiyori's primary motivation throughout the series is simple and consistent. She seeks to enjoy her time with her friends, eat her snacks, and avoid unnecessary emotional melodrama, which she finds bothersome as it interferes with her desire for a peaceful and fun school life. Her development is subtle, shown through her growing acceptance and understanding of her friends' romantic lives, moving from initial awkwardness to becoming a reliable and perceptive ally who provides a grounded, neutral perspective within the group. Her notable abilities are not physical or intellectual, but social. She excels at being a loyal and uncomplicated friend, using her cheerful bluntness to cut through tension and her simple, food-focused priorities to keep the group grounded.