“Do you ever wonder how it works?” Tony asks one day, apropos of nothing.
Working with Tony means getting used to many strange and varied opening lines. And considering that this isn’t even close to the strangest one he’s heard, Bruce decides to just go with it. “Well, I might have, if I have any idea what it is,” he says.
“This,” Tony answers, tapping the arc reactor on his chest. “Ever wondered?”
Of course Bruce has. That thing is a scientific miracle, and whatever else Bruce is, he’s a scientist first. He’s been itching to get his hands on the reactor ever since Tony first drew his attention to it, that day on the hellicarrier. Not to do any harm, just to take it apart to see how it works, and how the parts fit together to create something that can keep Tony Stark alive.
He’s never asked, though, because it seems a bit rude, and Tony had been kind enough to refrain from asking about the super-soldier formula that created the Hulk. Though, on second thought, Tony probably didn’t feel the need to ask and just got the files from SHIELD servers instead.
“Yeah, of course I have,” says Bruce. “Why?”
“Want to find out?” Tony says, grinning the way he does when he’s working on something and it’s actually giving that genius brain of his a bit of a challenge.
Bruce nods, smiling back, because at times like these, Tony’s enthusiasm is electrifying. He knows that whatever it is Tony is up to, it’s going to be amazing - it always is when he gets like this - and sometimes he’s just excited to be part of it.
Tony taps the glass display in front of him, swipes his fingers in Bruce’s direction, and an encrypted file appears on the screen in front of him.
“It’s voice activated,” Tony says. “Right now, it’s locked on your voice, and mine, of course.”
Bruce instructs JARVIS to display the files, and immediately, a 3D model of the arc reactor appears in front of him, along with the schematics and calculations and algorithms that form the base-code of the device. The physics involved in the making the arc reactor is mind-bogglingly complex, but the mathematics – the parts that he could actually understand, anyway – is beautiful.
He spends the best part of an hour examining the files, and he’s never appreciated the interface in Tony’s lab more. The 3D hologram allows him to see the device in perfect clarity, right to the minute details, and quite frankly, it’s astonishing.
“I can’t believe you built something like this out of scraps,” he says, finally, breaking the silence that he didn’t even realise had fallen in the lab. “It’s incredible.”
“It is,” Tony agrees readily, not being smug, but simply stating a fact. “But, you know, necessity, invention, blah, blah.”
Bruce waves the hologram away, turning to face Tony fully. “Tell me.”
Tony raises his eyebrow. “Everything’s there, in the files.”
“The files say what you did,” Bruce says. “They don’t say how you did it. So, tell me.”
Bruce turns contrite suddenly, remembering that this probably isn’t something Tony wants to relieve. “If you want to, of course. I don’t mean to pry, really.”
“Hey, no, Banner, I like you being curious. I wouldn’t have brought it up if I can’t handle it,” Tony says, genuinely sounding like he means it. “Anyway, you need to know, since you’re going to be helping me build a new one.”
“A new one?” Bruce asks.
“Yup, more power, longer use, less likely to break down; the whole shebang,” Tony grins. “You in?”
“Definitely,” Bruce says.
“Okay, so, you know about Afghanistan, I assume?” Tony says flippantly, as if it’s no big deal.
Bruce doesn’t buy it for a second, but he lets it go. “Some of it, yeah.”
“Well, some shrapnel got past my kevlar, and by the way, how rubbish is that? A bulletproof vest that’s not bulletproof. Hmm, got to start working on that,” Tony says, tangentially. “Anyway, the shrapnel were crawling their way into my heart, and from what I’ve heard, I had a week to live, maybe less.”
“The walking dead,” Bruce says, to Tony's obvious surprise. “I’ve heard about them, going around the world.”
“Huh. That’s what he said, too. Yinsen, the guy who saved my life. This,” Tony says, tapping his arc reactor, “This isn’t all me. It was his idea, originally, but he powered it with a car battery.”
Bruce blinks, making sure he’s heard right. “Wow.”
“Yeah. And it was a brilliant idea, actually.” Tony pauses, looking lost in thought. “Kidnapped and held in the middle of nowhere, he still came up with something like this. Freaking genius, too, he was. He helped me put together my first suit.”
Something flickered in Tony’s eyes, then. Something fierce and dark and familiar, something that Bruce dreads seeing in the mirror, sometimes.
“And he gave his life for it,” comes the quiet explanation.
And oh. Oh. No wonder Tony never talks about this. He’ll talk about the arc reactor freely enough, and the Iron Man suits, too, to anyone who asks. The press, the team, sometimes even SHIELD. But what he doesn’t talk about is this, the reason he built them in the first place, and the man who helped him do it.
Bruce doesn’t know what to say, really. He’s been out of touch with human interactions for so long that he’s still awkward in the best of situations, never mind something like this. “What was he like?”
“Oh, you would have liked him, Bruce. The guy was amazing. Engineering, tech, bio-chemistry, damn, I would have made him head of R&D in a heartbeat,” Tony says, smiling now. A touch wistfully maybe, but a real smile nonetheless. “And the amount of languages he knew. Hell, the only person who even comes close is, well, you.”
And Bruce? He takes it as a compliment, to be compared favourably to someone Tony obviously respects. So he nods, and says, “Yeah, you’re right. I think I would have liked him, very much.”
“All right, let’s go build me a new heart,” Tony says, almost gleefully.
Huh. A new heart. He hasn’t thought of it like that, but when Tony puts it that way, Bruce realises just how much trust Tony is putting in him. He is, quite literally, putting his heart in Bruce’s hands, and that, that settles like a weight on Bruce’s shoulders.
Not an unwanted one, not this, but a burden nevertheless. Because he still can’t figure out why this brilliant, lonely man trusts him so much, but he promises himself that he’d do anything to keep it. Because for him, and for Tony, too, there have been too many things broken already, shattered beyond repair. And he vows that this trust - this shining, fragile thing - will not be one of them.