Alphonse Elric saw everything.
He saw his brother when he was bruised, bloody, and broken. And he saw his brother when he was beaming with well-earned pride.
He saw his brother when he was laughing, fighting, running, screaming, begging, eating, smiling, yearning, missing, feeling, bleeding, whining, everything.
Alphonse watched his brother cry. He watched his brother fall and stand back up, only to slip again.
Then Alphonse saw his brother die.
It was one stab, clean and straight through. One blade, one homunculi, one mistake, in one empty room, was enough to kill Edward Elric. His eyes dilated, and his lips shaped the last words noone would ever hear. Then he was dead. He wouldn't rise, or blink, and Winry couldn't fix him. He was lost and truly gone, at least for that brief moment before Alphonse decided to bring him back.
In minutes Edward's glassy eyes cleared and newly formed tears overflowed onto his face. He placed shaking hands onto the smooth stone floor and he got up. He got up and he moved forward.
Alphonse Elric saw everything.
He saw his brother flex his right arm, brand new muscles and fingers. He saw his brother speak comforting words to Rose to get her to leave the abandoned city and wait for him up above. He watched his brother clap his hands and tap the floor, spreading new intricate circles onto he ceiling and floor and walls. Alphonse saw his brother walk, more calm and resigned than he's ever moved before. And when Edward reached the middle of the circle, Alphonse heard him whisper, getting louder at every word until he was screaming.
"...Alphonse...," he started, "Alphonse, I'm gonna get you your body back, and your soul too. I'm gonna get you back. You're gonna live. Damnit Al, you're gonna live if it kills me."
Then Alphonse saw Edward bring his hands together, and begin to glow. He watched his brother fade away, and he felt the memories, the experiences, the years they shared all slowly being pulled from his mind.
He woke up alone on the stone floor in a cold empty room. He didn't know why, but a few words kept circulating in his mind. 'Ed was lost to him. Ed was truly gone.' He didn't believe it, or them. Edward was alive out there, somewhere. And Alphonse was gonna get him back. He'd see Ed again. He'd find Ed even if it killed him.
Yeah, Alphonse saw everything.