Pinoko emerges from Osamu Tezuka's *Black Jack* series as a teratogenous cystoma, a rare Siamese twin who matured inside a patient's body for eighteen years. The unlicensed surgeon Black Jack extracted her surgically and crafted her an artificial plastic body. Following rejection by her biological twin sister, she moved in with Black Jack. Though physically resembling a young child, she retains her chronological age of eighteen and declares herself Black Jack’s fiancée, while he treats her paternally. She handles domestic duties for him and occasionally assists during surgical operations, providing comic relief through exaggerated outbursts like "Oh my Gewdness!"

As a recurring figure in Tezuka’s "Star System," Pinoko appears in multiple works, such as the 2000 special *Tezuka Osamu ga Kieta?! 20 Seiki Saigo no Kaijiken*. Here, she joins a New Year’s Eve assembly of Tezuka’s characters at Dr. Tenma’s mansion to investigate Osamu Tezuka’s disappearance, maintaining her established persona.

Her personality blends childlike enthusiasm with insistent proclamations of adulthood. She demonstrates jealousy toward women who engage with Black Jack and maintains a close bond with the character Sharaku. Her core traits persist consistently across appearances, with ensemble stories like the 2000 special underscoring her place within Tezuka’s expansive narrative universe.