Kaori Makimura, originally born Kaori Hisaishi, is the adoptive younger sister of Hideyuki Makimura. After Hideyuki, who served as Ryo Saeba's partner, was killed, Kaori took his place as Ryo's partner in the City Hunter business. She was adopted into the Makimura family as an infant after her biological father, a criminal, died. Though she later learns she is not Hideyuki's biological sister, she continues to regard him as family.

Kaori has a strong and assertive personality, often described as a tomboy. She prefers practical, masculine clothing such as suits and pants, which sometimes leads others to mistake her for a man. Despite this, she possesses a feminine side that becomes apparent when she dresses up, revealing a strikingly beautiful appearance. She is kind, caring, and fiercely loyal to her friends and clients. At the same time, she can be quick-tempered and jealous, especially when Ryo flirts with other women. This jealousy often manifests in physical comedy: she stops Ryo's lecherous behavior by striking him with a giant hammer, typically marked as weighing 100 tons. She serves as the voice of reason in their partnership, frequently reining in Ryo's reckless impulses.

Her primary motivation is to continue the work her brother began, upholding justice as part of the City Hunter team. She also cares deeply for Ryo and wishes to protect him, though she is reluctant to openly admit her feelings. Her role in the City Hunter operation includes handling client acquisition, managerial tasks, cooking, and defending female clients from Ryo's less honorable intentions. She is Ryo's partner and eventual love interest, and their relationship develops gradually throughout the series, marked by unspoken affection and mutual respect.

Kaori's key relationships include her deceased adoptive brother Hideyuki, whose memory drives her to carry on his mission. She works alongside Ryo Saeba, the City Hunter himself, and the two share a complex bond that mixes professionalism, friendship, and romantic tension. She also trains under Umibozu, a fellow sweeper, learning to set traps and plant explosives. These skills, along with her own resourcefulness, allow her to contribute meaningfully to missions despite lacking Ryo's combat prowess.

Over the course of the series, Kaori grows more confident and capable. She becomes proficient in trap-setting, often surprising even seasoned opponents. She also learns to better manage her emotions and trust in her own abilities. A notable element of her development involves her firearm: she carries her brother's revolver, but Ryo secretly tampered with it so that she would always miss her target, wanting to spare her from ever having to kill. When Kaori discovers this, she is deeply hurt, but the incident ultimately strengthens their partnership, and Ryo later restores the gun to proper working order while promising to ensure she never has to take a life.

Her notable abilities include trap-setting, explosives handling, and using a variety of oversized blunt weapons, most famously the giant hammer. She is also a capable cook and organizer. While her marksmanship is hampered by the tampered gun, she is otherwise resourceful in field operations. Her courage and determination often prove more important than raw combat skill.