Kaori is introduced in the aftermath of Akira's psychic destruction of Neo-Tokyo. She is one of the many survivors struggling to live in the lawless wasteland that remains. Her initial appearance reflects this harsh reality, as she is seen wearing ragged, dirty clothes and a scarf. Her entry into the main story occurs when she approaches an agent of the Great Tokyo Empire, the territory claimed by the powerful and increasingly unstable Tetsuo Shima, to beg for medicine and food to help her ailing father. Desperate and vulnerable, she is coerced into joining the Empire as one of several young women intended to serve as Tetsuo's sex slaves.

In terms of personality, Kaori is defined by her shy and timid nature. Despite her fear and difficult circumstances, she possesses a core of kindness and compassion. This is demonstrated starkly when Tetsuo distributes a powerful drug to his concubines; mistaking it for medicine, Kaori saves her portion to give to her sick father. This act of care, born from misunderstanding, inadvertently saves her life, as the other girls fatally overdose. Her gentle and motherly demeanor does not go unnoticed. While she is initially just another victim of Tetsuo's power, her personality eventually earns her a unique and sincere place in his affections. She becomes his closest confidant and the primary person he turns to for emotional support and comfort, particularly during the intense physical and mental strain caused by his rapidly evolving psychic powers. Furthermore, her kind nature leads her to be appointed as Akira's caretaker, a role she performs with patience, feeding and looking after the powerful, childlike psychic despite his often displeased reactions.

Kaori's role in the narrative is crucially tied to Tetsuo. She serves as the primary reminder of his remaining humanity, representing an emotional bond that he is still capable of forming. Her primary motivation shifts over time from simply surviving and caring for her father to a deep-seated desire to protect and be there for Tetsuo, whom she sees beyond his monstrous actions. Her key relationships are therefore almost exclusively with Tetsuo and his circle. As his emotional anchor, she is often called upon to calm him down after one of his destructive rampages. She also develops a relationship with Akira as his babysitter, her duties including feeding, playing with, and tucking him into bed.

Her development is tragically cut short. As Tetsuo's psychic instability grows, a conspiracy forms among his own aides, who plan to overthrow and assassinate him. Kaori, in a moment of loyalty and bravery, overhears these plans and attempts to rush to warn Tetsuo. While trying to save him, she is fatally shot in the back by one of the conspirators, Kaminari, to prevent her from delivering her warning. Her death has a profound and devastating effect on Tetsuo. Upon learning what happened, he kills the conspirators in a fit of rage and grief. Overwhelmed by the loss of the only person who offered him genuine, unconditional comfort, he desperately tries to use his immense psychic powers to resurrect her. This attempt fails, and in a final, sorrowful act, he carries her body to Akira's former cryogenic chamber in an attempt to preserve her. Kaori does not possess any notable supernatural or combat abilities; her strengths are purely emotional and psychological, defined by her resilience, her capacity for unconditional care, and her role as the fragile, human heart of a character consumed by god-like power.