Kaori Makimura, whose birth name is Kaori Hisaishi, has a complex background rooted in tragedy and adoption. After the death of her biological father, a criminal named Junichi Hisaishi, she was taken in and adopted by the family of detective Hideyuki Makimura. She was living as a nursing student when her adoptive brother, Hideyuki, was killed. Following his death, she inherited his Smith & Wesson Model 36 revolver and took his place as the partner of the private eye Ryo Saeba, forming the core of the City Hunter team. Her birthday is March 31st, and she is known to be 168 centimeters tall.

In terms of personality, Kaori is a quintessential tomboy. She typically presents herself in a masculine fashion, with short hair and practical clothing like pants and jackets, which often leads to her being mistaken for a handsome young man. Despite this, she possesses a traditionally beautiful appearance when she chooses to dress up. She is defined by her courage, strong will, and profound sense of generosity, always putting herself at risk to protect those she cares about. She is also highly emotional and business-minded, serving as a serious foil to her partner's frivolous nature.

Her primary motivation stems from her loyalty to her late brother and her deep, unspoken love for Ryo. She is driven to be an effective partner, taking on the managerial tasks of their business such as finding clients, while also striving to become strong enough to stand beside Ryo in his dangerous world. A significant part of her daily motivation is keeping Ryo's rampant womanizing and skirt-chasing in check, which she does with extreme prejudice.

Within the story, Kaori acts as the anchor and conscience of the City Hunter operation. She is the one who interfaces with clients and keeps Ryo focused on the job at hand. More importantly, she acts as his moral compass, using overwhelming force to prevent him from taking advantage of female clients. Her role evolves from a novice avenging her brother to a capable partner, and her romantic relationship with Ryo is a central thread of the narrative, culminating in an implied marriage by the end of the original manga.

Her key relationships define her journey. Her bond with her adoptive brother, Hideyuki Makimura, is a powerful, protective influence that sets her on her path. Her complex partnership with Ryo Saeba is the heart of the series, characterized by bickering, shared danger, and a deep, often unspoken, romantic love. She also has a meaningful mentorship with the mercenary Umibozu, who trains her in trap-making and demolitions. She discovers she has a biological older sister, Sayuri Tachiki, who initially seeks to reunite with her but ultimately decides Kaori's place is with Ryo. In the alternate continuity of "Angel Heart," Kaori dies in an accident and becomes an organ donor; her heart is transplanted into a young woman named Xiang Ying, and Kaori's lingering presence serves as a spiritual guide for her.

Kaori undergoes significant development, growing from a somewhat inexperienced and hot-headed young woman into a shrewd and capable partner. While her combat skills never reach Ryo's level, she hones unique talents. She becomes an expert in setting complex booby traps, a skill learned from Umibozu, which she uses for both defense and to prank Ryo. Her proficiency with heavy weaponry, including grenades and bazookas, is also notable.

Among her most notable abilities are her proficiency with her signature oversized mallet, which she can swing with tremendous force and even throw like a boomerang, and her use of a bazooka for disciplinary purposes. She carries her inherited revolver, but its sights were secretly misaligned by Ryo to ensure she would never have to bear the emotional weight of killing a person, effectively limiting her marksmanship with it for his protection as much as hers. This handicap leads her to rely on her other, more destructive talents to make her presence felt in a fight.