Kimi Aoi is the older sister of the protagonist, Toori Aoi, and a student at the Musashi Ariadust Academy. Physically, she is a teenage girl with long, wavy, light brown hair often adorned with pieces of white cloth, dark brown eyes, and a figure described as mature for her age. She typically wears the standard school uniform, though after a particular battle, she adopts a more revealing version consisting of a tube top and the standard lower half of the uniform.

Her personality is characterized by a sharp tongue and a playful, high-tension attitude, often prioritizing her own amusement over taking situations seriously. She frequently badmouths her younger brother Toori for his foolish behavior. However, beneath this cruel exterior lies a deep and genuine care for him, and she possesses a surprisingly affectionate side. Her actions are largely driven by her role as Toori's sister, as she constantly supports him and understands how to help him when he is in trouble. This support was most evident after the death of Horizon Ariadust, when a grieving Toori fell into a deep depression. Unable to bear his state any longer, Kimi took drastic measures to shock him out of his stupor. She threw him out a window and forced him to fight for his life, ultimately helping him accept Horizon's death and begin to heal. This event is noted as the only time she ever cried, and it was for her brother's sadness. After this incident, she led her brother to the Asama shrine to form a contract with a deity, which is how she gained her unique abilities.

In the story, Kimi acts as a key emotional pillar for Toori. She may dislike being called by her real name and has a fear of ghosts, as well as being terrible at cooking. Her primary relationships are with her brother, whom she loves fiercely despite her harsh treatment of him, and with her teacher, Makiko Oriotorai, toward whom she has shown small gestures of kindness.

Kimi Aoi is a shirabyoushi, a practitioner of traditional Japanese dance, and her abilities are rooted in this art form. She entered into a contract with the god Ame-no-Uzume-no-Mikoto, the deity of dance and sensuality. Her combat style is almost entirely defensive, centered on her dancing. Her signature ability, known as the Dance of the Summit, is based on the principle that the only ones who can touch her are those she desires to wither for. While she dances, she generates a massive number of barriers decorated with flower crests that can block incoming attacks at incredible speeds. The effect of this ability persists as long as she continues her dance, making her an untouchable fortress despite her lack of offensive power. Furthermore, every action related to her performance, including the rhythm of her steps, putting on makeup, and her fashion choices, is considered an offering, ensuring her protective ability is constantly active.