Ai Kisugi is the youngest of the three Kisugi sisters who form the core of the Cat's Eye. She is a high school student with a boyish, energetic, and spunky personality that sets her apart from her more poised older siblings. Despite her youthful and sometimes naive demeanor, she possesses a genius-level IQ and serves as the team's technical specialist. Her role in the group is primarily that of a mechanic and inventor, as she is highly adept in mechanics, computer programming, and engineering, creating a wide array of gadgets and tools to facilitate her sisters' art heists.

While not the most athletic of the three, Ai compensates with exceptional agility and a mastery of operating various getaway vehicles, including helicopters, motorcycles, and cars. Her appearance is marked by short, dark hair and brown eyes, and she is often seen in casual attire or a distinctive orange leotard when on missions. She has a pet tabby kitten named Tiger and, like many her age, often daydreams about falling in love, though her tomboyish nature tends to take precedence.

Ai's motivations are deeply intertwined with the sisters' shared quest to recover the artworks belonging to their missing father, the painter Michael Heinz. As she was born after his disappearance, Ai has no personal memories of him, which makes her attachment to his memory and her desire to find him particularly strong, perhaps even more so than for her sisters who knew him. This personal stake drives her to apply her technical brilliance to every heist they plan.

Within the trio, Ai relates to her sisters as the youngest member. Her relationship with her middle sister, Hitomi, often involves lighthearted teasing about Hitomi's romantic troubles with the detective Toshio Utsumi, a dynamic that highlights Ai's more carefree and observant nature. Her dynamic with her eldest sister, Rui, is more that of a subordinate taking direction from the group's leader and strategist. Over the course of the story, Ai shows development from a fun-loving teenager into a more capable and reliable young woman, though she retains her core energetic and youthful perspective. Her technical skills remain her primary contribution, and her ability to appraise art is trusted completely by her sisters. She has notable vulnerabilities, including a strong fear of snakes, and despite her intelligence, she can sometimes make errors in her otherwise brilliant plans.