Ai Haibara is the pseudonym of Shiho Miyano, a former high-ranking scientist for the secret criminal organization known as the Black Organization, where she operated under the codename Sherry. Born to scientist parents who worked for the organization, she was raised within its ranks. After her parents died in a suspicious accident, the highly gifted Shiho was sent abroad for education and returned to Japan as a teenage prodigy, continuing her parents’ research. By the age of eighteen, she had developed the experimental poison APTX4869, a drug designed for untraceable assassinations that also has a rare side effect of shrinking the subject to a very young age. When the Black Organization murdered her older sister, Akemi Miyano, Shiho halted her research in protest and was imprisoned. Expecting to be killed, she swallowed a capsule of her own APTX4869. Instead of dying, her body regressed to that of a young child, allowing her to escape. She collapsed near the home of Shinichi Kudo and was found and taken in by Professor Hiroshi Agasa, who gave her the alias Ai Haibara to conceal her identity. She enrolled in Teitan Elementary School, joining the same class as Conan Edogawa—the shrunken form of Shinichi Kudo—and his friends, who call themselves the Detective Boys.

Haibara has a calm, cool, and often cynical demeanor, with a sharp, sarcastic wit that contrasts with her childlike appearance. She speaks and acts with the maturity of her true age, which makes her stand out among her peers. This guarded exterior is a result of her traumatic past and constant fear of being hunted by the Black Organization, especially the operatives Gin and Vermouth. Beneath this facade, she is deeply caring and protective, especially toward animals and the friends she has come to value. Over time, she has formed genuine bonds with Professor Agasa, Conan, and the other Detective Boys, whom she considers her first true friends. She also has hidden, more childlike interests, including a fondness for fashion brands like Prada, an admiration for soccer player Ryusuke Higo, and a nostalgic taste for peanut butter and blueberry jam sandwiches from her time in the United States.

Haibara’s primary motivation is to live a peaceful life free from the Black Organization while protecting those she cares about. She works diligently to develop an antidote for APTX4869, using her scientific knowledge to help reverse the drug’s effects. In the story, she serves as a crucial ally to Conan Edogawa, being one of the few people who knows his true identity. She provides valuable information about the organization’s inner workings, uses her intellect to assist in investigations, and often acts as a voice of caution, tempering Conan’s reckless impulses. Her key relationships include her guardian-like bond with Professor Agasa, her complex and trusting partnership with Conan, her protective friendships with the Detective Boys, and her growing affection for Ran Mouri, who reminds her of her deceased sister. Throughout her journey, Haibara undergoes significant development, transitioning from a fatalistic and isolated fugitive to a more open and integrated young girl who learns to embrace her second chance at life. Her notable abilities include genius-level intellect in chemistry, pharmacology, and medicine; sharp deductive reasoning; proficiency with computers; fluency in English; and a unique instinct to sense the presence of Black Organization members.