Kayoko Kubo is a supporting character who works as a waitress, and at times seems to act as an unofficial assistant manager, at the family restaurant called Garden. She is a woman with a sharp tongue and a strong-willed, often harsh, personality who does not hesitate to bark orders at her coworkers. Physically, she is recognized by her black hair, which she almost always keeps tied up in a ponytail, her half-lidded eyes, and her large diamond-shaped mouth.

Her primary role within the story is as a senior member of the restaurant staff. She serves as a pragmatic and no-nonsense mentor to the younger employees, particularly the protagonist Akira Tachibana, offering help and practical advice when it is needed. At the same time, she is highly critical of her superior, the restaurant manager Masami Kondou. She frequently chides him for what she perceives as a weak and unreliable character, complaining about his performance and showing him little respect. She often voices her gripes to Tachibana regarding Kondou's inadequacy as well as her dissatisfaction with her salary and work benefits.

Despite this tough and sometimes cynical exterior, Kubo possesses a softer side that manifests in specific situations. She has a notable soft spot for children and small animals, which is most clearly shown through her kindness towards Kondou's young son, Yuuto Kondou. This gentle treatment of the boy stands in stark contrast to her usual stern demeanor with his father and other adults, creating a charming and humanizing aspect of her character. Furthermore, while she often projects an image of someone who is merely going through the motions of her job, she is not immune to emotional connections with her peers. During the farewell party for fellow waitress Yui Nishida, Kubo was visibly and openly saddened by her colleague's departure, revealing a more sentimental and emotionally vulnerable side that she usually keeps hidden.

Her development is subtle but present, primarily shown through the gradual revelation of these contrasting layers. She starts as a character defined by her gruff complaints about work and her disdain for Kondou, but the narrative reveals her capacity for mentorship, kindness to the innocent, and genuine care for her work friends. Her motivations are rooted in a desire for competence and reliability in her workplace, which is why Kondou’s lack thereof frustrates her so much. In terms of abilities, Kubo does not possess any special skills outside of her competence as an experienced waitress, being efficient and knowledgeable about the restaurant's operations, which is the source of her authority to mentor newer staff and critique her manager.