She moves with a grace unprecedented. He takes this as fact – no one has ever danced the way Natasha does, and no one ever will.

They used to do this every Thursday night without fail. But now it's a rare occurrence. The two of them spar, pitted against one another in a room of fluorescent lights and the smell of metal, sweat, skin. One jab. Hah. Duck. Hmph. Sway. Ahh. Bend. Breathe.

God, it's like praying.

Natasha's safehouse basement is reserved for this purpose: training. Exercise equipment litters every inch of the hardwood – an elliptical machine, a Stair Master, targets shredded with bullets, jump ropes and boxing gloves set next to a punchbag. She comes down here when she's tired of playing savior, when she wants to remember what her hands and feet can do.

A steady, bass-heavy rock music blares from a speaker system in the corner. Clint doesn't know the band. Natasha is into some obscure stuff from the postmodern underground, songs in strange languages; gruff sounds; electronic trills. Most of the words, he can't understand. But the music cuts through his hearing aids cool and clear – he can feel the beat vibrate in his bones.

It feels good. This all feels good.

He's getting his ass kicked, but that's normal. Natasha lets him have it, all of it, and he takes the hits like a good partner. She socks a punch against his jaw, whips around and snaps a knee into his stomach. He's quick enough to dodge her next jab, though, and he catches her forearm in his fist.

"Ooh. Getting sloppy there," he teases.

She replies by sweeping his feet out from underneath him.

They fight like angry lovers. It's brutal; borderline vicious. There's blood dripping from the corner of her lip, and he's got enough bruises on his chest to warrant a trip to the Night Nurse. Still, neither of them let up, not even for a second. Natasha is angry – furious, even – and she needs to give up that energy before it destroys her. Clint is simply lost, and when he's lost he goes to her.

This is them. No holds barred. It isn't a pretty picture. But it's them.

Natasha's rage slips from her system, as if she simply has to bleed it out. Cauterize the wound. Ignore the pain. Wait until the spark fizzles. A failed mission always puts her in a foul mood.

And while she outwardly appears controlled and collected, Clint knows failure wreaks havoc on her mind. Failure is what sends her old demons screeching from their cages. Doubt in herself, in her worthiness, in her goodness – it's her weakness. Perhaps it's the only vulnerability capable of crippling her.

Clint lets her put it all on him. He retaliates with his own brand of poison, his annoying quips, so that she feels some satisfaction when she whacks him across the face. He slowly draws the monster out of her.

In return, Natasha gives him hope. Natasha gives him a reason to believe in his own ability.

This is how they heal.

Smack. Rah! Punch. Mmff. Sigh.

As the minutes tick by in silent surrender, Clint wonders how many other men have had the privilege of training with Natasha. The legendary Black Widow. He knows of a few of them – Bucky Barnes, Steve Rogers, Matt Murdock. All better fighters than Clint. All better men.

Can you imagine? Matt Murdock. A blind man, a man with no fear, able to hear heartbeats. Matt couldn't even see Natasha, her blinding beauty, but could only sense it. He would know her only by her movements; by her agile turns, the way her lungs expand and her muscles strain. Matt Murdock would know Natasha more intimately than Clint ever could – the times when her heart skips a beat, the tiny fractures beneath her skin, the way she smells from a mile away.

Clint almost smiles at the thought of this; how lucky could a man get? To know this woman – even rarely, on the days she allows – is to know a piece of Providence.

Suddenly, as Clint and Natasha's arms meet in the air, the music changes. Clint still doesn't know the song or the artist – he and his brother weren't exactly music connoisseurs in their youth. "Baba O'Reilly" and "Champagne Supernova" were the only mixtape tracks they knew by heart. So Clint loses his balance when Natasha's speaker system shifts from hot and heavy rock to something quiet and gentle. It's soft, almost timid; the tinny, raw sounds of guitar strings. They seem to tremble through the room, unseen but omnipresent.

Then there's piano. Something in a major chord? Hell, Clint doesn't know.

Natasha is caught off-guard. She stops for the first time in an hour, chest heaving as a bead of sweat trails down her neck; it disappears beneath the collar of her shirt. She stares at Clint, saying nothing.

They don't have to speak. They both realize at the same time: this is one of the old songs. The ballet songs from the Red Room. Before everything changed.

Natasha stands there for a moment, her hands on her hips. Clint is hesitant, lost to find words to break the tension. Neither of them enjoy discussing years gone by; it always feels too weighted, too controversial. Natasha was a very different person when this song was part of her repertoire, and Clint had only just met her.

Feeling a little bashful as the song dips into melody, Clint clears his throat.

"I, uh … I'm gonna go. You want to meet again tomorrow morning? We can head down to Fogwell's if you want, I was gonna—"

Then she steps forward. He can already see the fever break in her eyes. He knows that look too well – this is her venom.

Oh, God.

"Dance with me," she says. It's more of an order than a request.

He's two seconds away from refusing – it would be the smart thing to do. He's a terrible dancer anyway; nearly tripped over his date's toes at high school prom. But this is Natasha – who dances like a swan, who commands the earth beneath her. She doesn't need superpowers to control the minds of men. That's just who she is.

So it isn't seductive, the way Natasha's hands move up Clint's shoulders and meet behind his neck. Her breath against his ear isn't chilling; it's oddly comforting. It's as if she's guiding him, one silver lining to another. Step … by … step. This is just another part of their training.

But. Clint thinks he can feel her heartbeat against his chest. And it might be just a little faster than normal.

Maybe.

She closes her eyes and begins to sway. He doesn't know what to do with her body, with her hips beneath his hands. She bends and he supports her, keeps her light on her feet, and they move together. There's a tinge of a smile on her lips, like this is all part of her plan. Clint watches her, terrified and unsure and yet completely comfortable. He is dancing with Natasha. His partner. His best friend.

She unfolds like an iron rose. One petal at a time.

Natasha moves out of his grasp, her eyes still closed. Standing in the middle of the room, he watches her practice her art. Skin as thin as paper, light streaming over her hair. He can see right through her, to a heart the shape of a black hole. She never was a ballerina in Russia – that was all a trick, a lie – but that doesn't mean she isn't the loveliest prima donna Clint's ever seen.

Her arms lift above her head in a perfect oval, fingertips meeting like shy kisses. She's wearing sneakers instead of slippers, but she's en pointe, her whole body arched towards the sky. She turns in time with the music, her weight shifting with the strums, arching with the press of each key. And Clint wishes he could capture this moment. He wishes time didn't inevitably run out. It's a crime that this only happens once or twice a year. More people should know her for her gentleness; not for her deathliness.

Bend. Strum. Lift. Strum. Twirl. Strum.

This is only the second time he's ever seen her dance. The first time was when he decided to save her life.

Her eyes open and they are as clear as the night sky. She moves back to him, shimmering a little, a desert mirage or a – a ghost or – it's probably just the foggy lighting and the sleep deprivation, but—

Natasha takes both of his hands in her own. His fingers alone are huge compared to hers, callused and cut from multiple arrow nicks. Hers somehow remain delicate and manicured, no matter how many triggers she pulls in a day. This is her magic. She never allows the world to break her.

"I told you to dance with me," she says. She's placing one of his hands on her waist, the other along her back. He accidentally catches a few tendrils of her long, sweet-smelling hair in his grip.

"Yeah." He swallows. "Yeah, sure."

And so they dance. Something like a waltz, but not quite. More of a sway. Their faces are close, their breath mingling, and the whole world is on a tightrope.

They both know. They both know what's about to happen.

It's been years since they dated. They haven't even shared a bed in months, maybe even – has it been a year now? Clint doesn't know. But they've just been friends for such a long time now, friends with the occasional flirtation, just a casual gesture to show respect and admiration. They care about each other, that much is obvious, but … what kind of territory is this? This is dangerous. This is …

Is this love? Do either of them even understand love?

How can Clint be what she needs? How can they do this to one another – tying together glass souls and hoping they stick? It's too risky, too unpredictable. They aren't even compatible – Clint is too loud and reckless, Natasha too cold and alone.

Love moves in mysterious ways.

No stopping it now. She leans forward; his breath hitches. Their foreheads are touching, and they stand against one another, silent as the music fades.

Then gently, so gently he almost doesn't feel it … she kisses him. Her lips brush against his. He can taste mint on her breath.

Testing the waters. Is this real? Is this okay?

Yes? Okay.

Natasha unfolds, and Clint bends with her. Their lips meet as she collapses against him, her arms tying around his neck. Sweet, sweet kisses. Deep kisses. He hasn't kissed her in so long. He almost forgot what she smells like – the cinnamon scent of her skin, the tealeaves on her tongue from the Russian Caravan she drinks at lunch. And she gathers the same from him, the soapy smell of his hair, the way he reacts to her breathing. It takes a moment for his hearing aids to adjust to something so soft.

He lifts her into the air, her legs wrapping around his waist. Their tongues meet, and then they meet again, and the whole wonderful thing starts over again. They could be here for hours. And Clint doesn't need to be Matt Murdock to hear her heartbeat. It pulses against him, matching his own. They're in sync. He almost laughs.

"Thanks for the training," she whispers, her lips moving down his neck. She plants a kiss along his jaw, at his collarbone, on the bruise from her earlier punch. "And for the dance."

"Hey," Clint replies, a little shaky. "Any time."

Fixed in time, at this moment, they can ignore the world crumbling around them. They can ignore the colliding universes, the timelines and the storylines that conflict and cancel one another until there's nothing left. Of course Natasha is afraid – to lose herself, after so many years building herself up? What greater sin is there? Ultron has the potential to rip away everything she's learned to care about. And Clint? He worries he's helpless to stop it.

They hold one to another, even as fearsome odds surround them.

"Tomorrow, I'm really going to kick your ass," Natasha whispers. She kisses his cheek and winks.

He looks back at her, steadfast and smiling.

"I wouldn't have it any other way."