Automail

Within the setting, automail refers to motorized armored prosthetics that stand in for missing body parts. Its roots trace back to a kind of powered fighting armor, but the technology matured into limb replacements far more capable than the plain prosthetics amputees would otherwise settle for. The kanji reading translates roughly to mechanical armor, and some sources render the name as auto-mail.

What sets automail apart is its wiring into the nervous system. Because it draws its cues directly from the body's own nerve signals, the limb needs no outside power supply and answers to the wearer's intent just like a real arm or leg. Those nerve pulses drive the electric motors and pneumatic parts packed inside the frame.

Construction typically centers on a complete steel skeleton wrapped in steel plating that shields the delicate wiring and gears within. Newer engineering has broadened the material list well past steel, folding in carbon fiber, fiberglass, chrome, and assorted copper-nickel and aluminum blends to trim weight and better survive punishing environments.

Owning automail comes at a steep cost, which drives many amputees to avoid the upgrade entirely. Fitting it demands a specialist versed in both mechanical engineering and surgery, and the procedure is both pricey and brutal. Surgeons frequently have to trim away more of the limb to seat the hardware, and the raw nerves read every jolt of the process as searing pain. Each nerve gets bound into a fixed port on the body, and all of them must link up at once when the limb is joined to that port.

Adjusting to a new limb usually eats up around three years of recovery and training, though faster cases exist, with Edward Elric managing roughly a year and Lan Fan reportedly only six months. Even afterward the machinery needs constant care, regular oiling and periodic teardowns that force the parts to be unhooked from and then agonizingly reconnected to the nerves. Wearers also suffer aches when air pressure swings sharply. Steel limbs bring their own weather troubles: in blistering heat the metal traps warmth against the skin, while deep cold thickens the lubricating oils and hastens frostbite in the connecting tissue. Engineer Dominic LeCoulte notes a further downside, that automail taxes a young body's physical development and can stunt growth.

Inside Amestris, where decades of back-to-back wars fueled demand, the craft branched into combat automail. Builders began arming these limbs with diamond-tipped claws, concealed blades, and even guns, sometimes trading away ordinary hand function to do it. A subculture of enthusiasts even opts to surgically remove healthy flesh in order to acquire weaponized versions. Rarer still are so-called full-body automail that replace vital organs and make up much of a person's frame, a concept shown chiefly in the 2003 anime and only hinted at in the manga.

Edward Elric is the series lead and wears a right arm and left leg crafted by his childhood friend Winry Rockbell. After his original steel set is wrecked, she rebuilds it with added chrome for rust resistance, and for the frozen north he switches to featherweight aluminum-and-carbon-fiber models. By the end of the story he recovers his real arm but keeps the automail leg. Lan Fan, after losing her left arm in battle, receives a combat replacement fitted with a spiked band around the hand and a long blade jutting from the elbow.

Several others rely on it as well. Bald of the Blue Squad hides a double-barreled rifle and an army knife inside his left arm. The Rockbell dog Den has an automail front leg, while Paninya walks on two automail legs built by Dominic LeCoulte, one concealing a blade and the other a small cannon. Captain Buccaneer of Fort Briggs swaps between combat arms including the M1913-A Crocodile and the M1910 Mad Bear Grade. Young Tetsu of Rush Valley leans on an automail leg from Winry. Other appearances stay tied to specific adaptations, such as Frank Archer and the homunculus Wrath in the 2003 anime, Genz Bresslau from a video game, and Julia Crichton from the film The Sacred Star of Milos.