Kaori Makimura is a central figure in Angel Heart, though her role is defined by a profound absence. Born as Kaori Hisaishi, she was adopted into the Makimura family as an infant after her biological father, a criminal, died in an accident. She grew up alongside her adoptive older brother, Hideyuki Makimura, forming a close bond with him. As a young woman training as a nursing student, she met Ryo Saeba when she saved his life by treating a gunshot wound, an encounter that would permanently link their fates. Following her brother Hideyuki's death, Kaori took his place as Ryo's partner, helping to form the City Hunter team that took on dangerous cases in the shadows of Shinjuku.

In terms of personality, Kaori is characterized by her tomboyish appearance and straightforward, sometimes aggressive nature. She is deeply caring and loyal, but she does not hesitate to express frustration, particularly regarding Ryo Saeba's constant womanizing. Her signature response to his flirtatious behavior is to produce impossibly large mallets or a bazooka to strike him down, a comedic display of her irritation and hidden jealousy. Despite these outbursts, she is a capable and responsible partner who primarily handles the managerial side of the City Hunter operation, such as arranging clients and maintaining their base of operations.

Her primary motivation is her love for Ryo Saeba and her commitment to the mission they inherited from her brother. She wishes to protect the people of Shinjuku while also trying to keep Ryo focused and out of trouble. Her deep, unspoken romantic feelings for Ryo drive many of her actions, from her jealousy over his female clients to her steadfast refusal to leave his dangerous world, even when he tries to push her away to protect her. She is determined to remain by his side, providing both practical support and a moral anchor.

Within the story of Angel Heart, Kaori is not a living character but a powerful spiritual presence. Her heart was transplanted into a young assassin named Xiang Ying, also known as Glass Heart, after Kaori died in an accident. It was revealed that Kaori was a registered organ donor, and her heart saved Xiang Ying following a suicide attempt. Her personality and memories persist within Xiang Ying, manifesting through dreams and, at times, briefly taking control of the young girl's body to guide her or to comically scold Ryo. This connection makes Kaori a guiding force for Xiang Ying, who comes to view Kaori as a maternal figure and takes her place as Ryo's partner.

Key relationships define her life and legacy. Her bond with Ryo Saeba is the most significant, evolving from a working partnership into a deep, mutual romance that, by the end of their story, implies they were married. Her adoptive brother, Hideyuki Makimura, was a protective figure whose death she avenged by taking his place in the City Hunter team. She also shares a connection with her biological sister, Sayuri Tachiki, who ultimately chooses not to disrupt Kaori's life with Ryo. Kaori learned trap-making and demolition techniques from the mercenary Umibozu, a family friend.

Kaori undergoes notable development from a relatively inexperienced young woman into a confident and capable operative. She became proficient in setting complex traps and handling explosives, skills taught to her by Umibozu. While she carries her late brother's Smith & Wesson Model 36 revolver as a keepsake, her marksmanship is deliberately poor. Ryo modified the gun to ensure she would always miss her target, preventing her from having to kill anyone and keeping her hands clean of blood. Her true abilities lie in her logistical management, her trap-making, and her fearless, if comical, use of heavy artillery to keep her partner in line. Through her enduring presence in Xiang Ying, Kaori continues to influence the world of Angel Heart, her spirit acting as the emotional core that guides both the assassin and the sweeper.