Chapter 12: The Definition of Human

Ross and Brosh discover that the Elric brothers have vanished from their hotel room overnight and race, furious, to the most likely spot, the abandoned Laboratory 5. Inside, Edward's fight with Number 48 opens on even terms until a worrying twinge warns him something is wrong with his automail arm. Remembering Winry's caution that the new model is less durable than the old, he tries to finish quickly and instead finds himself dodging Slicer's escalating assault, gathering a scatter of small wounds. Number 48 praises the boy's agility but warns that mounting blood loss and exhaustion will be his undoing, adding that his partner outside is being dealt with the same way and will bring no rescue. Ed asks whether that ally is as strong as Slicer; told 66 ranks a close second, he laughs, since he has never once bested that partner in a fight.

True to his word, Alphonse plainly has the upper hand over Number 66, deflecting every wild swing until one blow knocks the helmet loose, exposing an empty shell. With theatrical flourish, 66 announces himself as Barry the Chopper, a butcher-turned-killer notorious in Central for twenty-three victims before his capture and supposed execution, which was only the official story; in truth his soul was torn out and bound to armor to guard the lab. Al reveals that he too is hollow inside and that, raised in the rural east, he has never heard of the capital's infamous murderers. Bristling at the assumption that he is another executed criminal, Al explains that his brother saved him by binding his soul to armor after his body disintegrated. Barry slyly twists this, proposing that Al's history and memories are fabrications of the alchemist who claims to be his brother; with the very existence of a soul in doubt and his body supposedly gone, what proof has Al that he was ever human beyond the word of others? As Al starts to doubt himself and demands how Barry can be so certain of his own existence under the same conditions, 66, after cutting down a soldier drawn by the noise, answers that the sheer joy he takes in killing is proof enough of his existence.

Back inside the lab, a clever feint lets Edward land a hit and sever 48's helmet, freeing the blood rune from the body's control. He begins interrogating the head about the Stone, only for the sword to plunge into his side from behind; the body has risen on its own. Number 48 reveals that the Slicer was in fact a pair of murdering brothers, and the younger one, speaking through the body, declares that his separate rune sits within the torso before charging so Ed cannot shape a fresh weapon. Wounded and seized by the dread of impending death, Ed recalls his encounter with Scar, claps his hands, and rather than transmuting the floor or his arm thrusts his palm at the attacker, using Scar's deconstruction method to blow the armored body apart at the waist.

Defeated, the elder Slicer asks Ed to finish them off. Ed insists he is no killer, and Slicer counters that only slaying humans qualifies as murder. With Alphonse straining harder against Barry, Ed tells Slicer that because he regards his brother as human, he regards the two of them as human as well. Amused, since the brothers were branded inhuman monsters throughout their long life of crime and only now are called human after losing their flesh and blood, the elder Slicer offers to share what he knows about the Stone and its makers. Before he can speak, however, a familiar pair of long dark blades impales his helmet as Lust steps from the shadows with Envy at her side.

Ed's failing automail nearly costs him the duel with Number 48, whom he ultimately splits apart using Scar's deconstruction technique. The Slicer is exposed as two soul-bound brothers rather than one. Barry the Chopper's true nature is revealed to Alphonse, and his taunts leave Al doubting whether his soul and childhood memories are genuine. Just as the elder Slicer prepares to disclose the truth about the Stone, Lust and Envy arrive and silence him.

This chapter marks the origin of the small scar above Edward's right eye. Its Japanese title reads "Ningen" no Teigi, and its events were later adapted in the 2009 anime series.