In the chaos of the fight, Bucky almost didn't see it happen. The crashes of Thor's hammer, the roars of the Hulk, blasts from Tony's suit, gunshots, explosions everywhere. But all at once, the sounds of battle were muffled in Bucky's ears as he saw Steve fall. He was barely aware that the eyes of the other Avengers had been pulled away from the fight and toward Steve as he rushed to his best friend's side.
"Steve! Steve, are you okay? Please be okay."
"Hey Bucky," was the feeble answer.
Bucky scanned his eyes across Steve's body, assessing the damage. The dark bloodstain on his chest was far too hard to miss.
"No…" he murmured.
"Bucky, I–"
"No, shut up, you're gonna be okay!" said Bucky desperately. "You have to be okay!"
Steve looked up at him with the saddest look in his eyes. As if the blood spreading across the front of his suit wasn't bad enough, that look broke Bucky's heart entirely.
"I'm sorry," said Steve quietly, barely audible over the sounds of the battle around them.
"You don't have to apologize for anything," Bucky said.
He gently put a hand on Steve's cheek, the real flesh-and-blood hand. Steve's breathing was getting weaker. He was fading out fast. Way too fast. Bucky blinked hard, trying to keep back the tears stinging his eyes.
"Steve please, hang on. We can do something, there's gotta be some way…"
"There isn't. You gotta keep fighting, Buck. You gotta win this," Steve whispered.
"I'll try."
Steve was too still, the silence too complete. Bucky's vision blurred as the tears beat his efforts to hold them off.
"Steve? Please, wake up, please."
Of course there was no answer. There couldn't be. Wouldn't be. Steve Rogers was dead and no amount of heart-break in Bucky's voice could stop that. Bucky closed his eyes and felt two hot tears tumble down his cheek. When he opened his eyes once again, he stared down at Steve, hoping, stupidly hoping, that it was all some horrible dream, that Steve was alive and fine and they'd get up and fight off these bullies just like they'd always done. But it wasn't a dream. It was all too real.
A throbbing hole seemed to have taken the place in Bucky's chest where his heart had been mere minutes ago. He leaned forward and placed a soft, lingering kiss on Steve's forehead. Unwilling to break what was likely his last moment of closeness to Steve, he hovered there, his forehead barely resting on Steve's, and whispered,
"Captain America's still gonna win this fight. I promise."
Slowly, he pulled himself away from Steve and stood up. Lying abandoned beside him was that famous iconic shield. Bucky reached down and picked it up, testing its weight on his arm. Then with one last glance down at Steve, he raced back into the fight.