They had known, at least in theory, what the brothers had been working so hard towards; but they hadn't really understood, not until that day.
Hawkeye counted it an honor that Edward even allowed them in the room when he'd done the transmutation, as difficult as it would have been to throw them out of their own facility. But that didn't keep them from standing shell-shocked and stunned around the perimeter of the room as the reaction faded, as Ed shouted something incoherent in triumph and fell—laughing—into the arms of the boy in the center of the circle.
They'd known, intellectually, that Alphonse Elric was the younger brother of Edward Elric; that there was a year between them, that Ed bossed his younger sibling around terribly, that the youth was insecure and deferential as a child sometimes.
But to them—even to Mustang, who'd known them the longest—Alphonse had never been anything but the hulking suit of armor. They'd grown accustomed to him as a person, or so they'd thought—his quirks, his childish voice, his oddly restrained and constrained motions in the oversize body; his cheerfulness and optimism, his serious responsibility, his love of cats.
Never in all that time had they seen past Alphonse-the-strange-but-endearing-armor into Alphonse-the-boy, the boy currently laughing and crying and hanging onto Edward's arms like his life depended on it. It was so strange—so strange—Alphonse was supposed to be the bigger of the two, hugely bigger than his brother, his hulking stature making the undersized alchemist look even tinier by comparison. But now they were the same size, or close enough to it, at least, that when they crushed each other into a hug they could wrap their whole bodies around it.
It was so strange, the way Alphonse's suddenly reduced size could make Edward look suddenly so much bigger, the older brother, as he cupped Alphonse's face in his hand, as they met eye to eye for the first time in years, years, as he shrugged out of his red coat (and his arms, his shoulders were so much bulkier than his brother's, that was the opposite of how it should be) and wrapped it around Alphonse's thin, new shoulders.
And it was so strange that at the same time Edward suddenly looked so much smaller, so much younger, as if measured against a normal teenager it suddenly became apparent how many years of growing up he still had left to him. Or maybe it was the expression on his face that made him look so young, so open and joyfully innocent, as he chattered on and on at his brother at such high speeds that with the two of them talking at once like this, they might as well have been talking in code.
It was Alphonse who had changed, so why was it that the Edward they knew suddenly looked so much different, as he embraced his brother tight, buried his face in a red-clad shoulder and gave a laugh that was oddly akin to a sob. And Alphonse, they had time to get a clear look at his eyes—not red, not odd pits of soulfire light, but an olive green-gold that complemented his looks and coloring perfectly—before he closed them, his hands rising gently to pat at his brother's back as a gentle smile split his face.
None of them had ever seen what Alphonse Elric looked like before—not even Colonel Mustang. Yet as he finally detangled himself, and stood up—one hand on his brother's shoulder, the other clutching the coat around him—and faced them, he looked just as he must. The blood resemblance was clear, so obvious that a stranger at a glance could tell that the two were brothers, and yet there were differences enough that he looked nothing like the 'smaller, gentler Edward' that their imaginations had always conjured.
He was a stranger to them, this boy, with the dark blond hair and the hazel eyes and the thin frame shrouded by the red coat; and he made Edward a stranger to them as well, hovering anxiously by Al's side, eyes and attention riveted only on him, ignoring the rest of them.
Alphonse did not. Unsteadily, he gave them a wobbly, but sincere bow of gratitude. "Thank you," he said, and when he spoke, the voice was the same, the voice was the same, except now it was clearer, closer, a little bit deeper. "Without your help, Niisan and I would have lost our way."
With every word he spoke, it startled them, enough that ghostly images of Alphonse-they-knew—gray, hulking steel—towered above him. When he spoke, it was hard to look through that illusion and see him as he really was, as he ought to have been.
But Edward's eyes, so clear and piercing in their love and loyalty, looked right through the gray haze and saw his brother whole, perfect, in his own body again, and with that look they understood, that this boy was what Edward had been seeing all along.