So, Howard and Maria were one of the Winter Soldier's missions, right? And he was even ordered to make it look like an accident? I can just imagine all the Bucky feels when this comes into the light, especially when he's mostly recovered and with the Avengers already. How would he and Tony react?

Bucky wasn’t exactly loquacious around the Tower with anyone, but he went dead silent around Tony. For Tony’s part, he wasn’t used to that. He was used to the extremes of attraction and antipathy, not cold blankness. It made him nervous and that made his jokes turn mean.

Bucky stayed silent.

Tony got louder.

Bucky grit his teeth but stayed silent.

Weeks went by like this, Tony ratcheting up and Bucky shutting down. Tony couldn’t put it into words but it pushed every button he had to have one of those war heroes his dad cried into his whiskey about staring him down with cold, blank eyes. It felt like the old neglect but with new edges and Tony could have screamed.

But it all came to a head after a particularly bad fight in which Bucky lost one of his metal fingers down the jaw of a giant alien with molten breath. Tony brought him back to the workshop and tried to chatter through the tension between them. If he made enough noise, Bucky might as well not be there, right? It could be like the same as the companionable silence when he was alone with his robots.

“Your father,” said Bucky suddenly, cutting off a particularly long-winded story about a rocket launcher and Tony’s fifth grade teacher.

And, woo, was that not the topic Tony wanted to get going on.

“—was your bestest bud, I’ve heard,” said Tony, filling the air ever faster. “Such a great guy, glad you agree, Steve’s favorite—”

“I killed him,” said Bucky, cold and blank. “I remember that now.”

Tony stuttered to a halt.

“….the breaks,” he said slowly, “you cut…the…brakes.”

“Yeah,” said Bucky, solid. Cold.

“Then you killed my mother too,” said Tony.

“Yeah,” repeated Bucky. He pulled the screwdriver out of Tony’s lax fingers, laid it on the bench, and snapped shut the panel Tony had opened in his arm. “I’ll take this somewhere else. I can be gone in an hour.”

Tony’s brain was still swirling around the new information, he could barely understand the words Bucky was saying.

“…why?” he asked, bewildered.

Bucky had already stood but he looked back down at Tony on his workbench.

“It was academic for you before,” he said. “Hypothetical. But I’m a killer, Tony. And I can’t make amends for that.”

“It wasn’t academic,” said Tony slowly. “It wasn’t personal, but it was never academic.” He picked the screwdriver back up and motioned for Bucky to sit down again.

Bucky came slowly. He clearly expected to be hurt, it was written as clear as day on his face. But he came back, sat down, and waited for it.

‘God,’ thought Tony, ‘he thinks he would deserve it if I tortured him right now.’

It made his stomach turn.

"Bucky,” he said, using the man’s actual name for the first time and not one of a thousand variations of vaguely insulting nicknames, “do you know what my kill count looks like?”

Bucky shook his head slowly.

“Yours is child’s play compared to mine,” said Tony. “You were handling yours personally, one by one. I went for whole towns. Armies.”

He flipped the panel back open.

“It was never academic,” he repeated.