Natsuko Aki, often called Nat-chan, is a major supporting character in the Cutie Honey franchise whose role and depiction shift notably across different versions. In the original 1973 manga and the early anime series, she is a student at Saint Chapel Academy, an all-girls school, where she serves as Honey Kisaragi's best friend and roommate. In these early incarnations, she is portrayed as a cheerful, loyal, and slightly mischievous schoolgirl whose primary function is to provide a grounding, everyday presence in Honey's life, unaware of her friend's secret identity as the android heroine Cutie Honey. Her background is that of an ordinary teenager, and her motivations revolve around friendship, school life, and the typical concerns of a young student.

A much more divergent version of Natsuko appears in the 2004 OVA series Re: Cutie Honey. There, she is reinvented as Aki Natsuko, a lead investigator for the National Police Security Task Force Branch 9. In this iteration, she is cold, controlling, and an absolute perfectionist, with a sharp, no-nonsense demeanor. She is an exceptional police officer and an expert marksman, but she has a tendency to get in over her head during investigations. Her personality in Re: Cutie Honey is marked by a hidden vulnerability: she lives alone in a small apartment, wears non-prescription glasses to downplay her appearance, and has a passion for Japanese sake that, when indulged, leads to uninhibited karaoke sessions. Her role in the story is that of a determined law enforcer who becomes aware of the masked vigilante Cutie Honey and attempts to arrest her, creating a professional conflict that eventually intertwines with Honey's world.

In other versions, such as the 1990s OVA Shin Cutie Honey and the 2018 series Cutie Honey Universe, Natsuko mostly returns to her original role as Honey's supportive friend and schoolmate, with occasional variations. Across the franchise, her key relationship is consistently with Honey Kisaragi, though the nature of that relationship varies from devoted school friend to adversarial-yet-reluctant ally. Her development is tied to the tone of each series: in lighter entries, she remains a static source of normalcy, while in darker interpretations like Re: Cutie Honey, she undergoes a more complex arc as a driven professional who must reconcile her duty with the truth about Honey. Notable abilities depend on the version: in her original form, she has no combat skills, but as a police officer in Re: Cutie Honey, she is a highly capable marksman and investigator, proficient in firearms and police procedure. She is tragically killed by Panther Claw in the original series and in Cutie Honey Universe, a fate that underscores her role as an innocent casualty in Honey's war against the criminal organization. Overall, Natsuko Aki functions as a narrative anchor, representing the human world that Honey protects, and her character adapts to fit the tone and setting of each installment in the franchise.