Haibara Ai, real name Shiho Miyano, is the creator of APTX 4869, the pill that shrunk Shinichi Kudo into Conan Edogawa, and a victim of it herself. Formerly Sherry of the Black Organization, she is on the run from them and lives with Professor Agasa. She is also one of the few characters who know that Shinichi is Conan.

To prevent the knowledge of her transfiguration from being discovered, Shiho and Professor Agasa create her alias Ai Haibara. As Ai Haibara, she attends Teitan Elementary School with Shinichi Kudo's shrunken form, Conan Edogawa. Following her first adventure with the Detective Boys, she reveals her true identity as the developer of APTX 4869 to Conan. Also accurately deduces Conan as Shinichi in the shrunken form, though her deduction is based on prior knowledge of her research and investigation of Shinichi Kudo. Conan protests her presence, but as time passes, he accepts her as a friend, though her cynicism and secretive air still rail him at times. Although she does not think too highly of the Detective Boys' immature antics, she has come to value them all as close friends.

Haibara has begun working on an antidote for the APTX 4869, but since most of the important data had been stored on computer files, which are now mostly destroyed, the work progresses slowly. Conan also eventually succeeds in persuading Vermouth to leave Haibara in peace after ruining a murderous plot. This fragile peace lasts until Sherry's whereabouts leak to the rest of the Black Organization and a second murder plot occurs aboard a train. A counter plan results in an explosion that preserves Shiho's secret identity. Currently all major Black Organization members besides Vermouth believe Sherry is dead.