Mary Steinberg, a skilled engineer focused on maintaining and modifying Extended individuals, carries a disheveled appearance: blonde hair braided at the back frames blue eyes set in fair, freckled skin, a lower lip piercing adding an edge to her sleep-deprived demeanor. Dirt smudges often stain her hands, evidence of relentless mechanical work.

Orphaned during wartime alongside brother Victor, their adoption by engineer Emmett shaped her path. Victor’s later disappearance during military service cemented her mechanical pursuits, fueling a relentless hope to reunite with him. This drive led her to operate from the unregulated Kyusei Pit, supplying cost-effective Extended components through mafia-linked channels.

Proficient in both mechanical and medical support for Extendeds, she repairs malfunctioning augmentations, installs functional limbs or vocal modules, and devises tailored fixes—like replicating specialized medicated cigarettes for a dependent client. Her toolkit includes twin mini rocket launchers hidden in her jacket lining, deployed strategically during firefights.

Critical missions involve replacing defective parts for a young Extended girl and aiding a private detective in safeguarding Tetsuro Arahabaki, a boy embedded with experimental neural tech. For Tetsuro, she installs mobility extensions, restoring his ability to walk and use arms while warning of lifelong maintenance. She intervenes in corporate skirmishes—disabling snipers, treating anti-Extended bullet wounds, and dissecting cybernetics tied to Victor’s research.

Colte, an Extended built with Victor’s components, becomes pivotal. After Colte’s demise, she salvages a part bearing Victor’s manufacturing signature, proof of his survival that sharpens her determination amid corporate clashes, even as injuries test her resilience.

Professionally pragmatic yet personally loyal, she challenges the detective’s ethics while providing tactical support. Her mentorship of Tetsuro blends technical rigor with emotional steadiness, guiding his adaptation to enhancements. Persistent themes orbit her—the morality of human mechanization, corporate exploitation, and war’s lingering scars. Her unresolved search for Victor mirrors society’s struggle with augmentation’s costs, each repaired Extended a step toward reconciling her fractured past.