Work Text:
The world is ending.
Izuku explains to Katsuki that the heat death of the universe is finally happening. That they—the world, the universe, whoever else is out there—are approaching a state of maximum entropy. That there remains little energy to be harnessed and used. It’s all falling apart.
It doesn’t mean shit to Katsuki.
All he knows is that hot showers have become a special treat, few and far between. That food is cold and hard and dry, because most of it is preserved and synthetic and best—worst—of all, edible without the need to cook it. That the rhythm of their days are mandated by the rise and fall of the dimming sun. The only electricity that runs through their little space powers Izuku’s computer—a privilege of his status as a researcher.
All he knows is that he’s lost count of how long this winter has been. They might as well stop calling it winter, because it implies that there is a spring, a summer—a change that could come. There isn’t.
Izuku says it’s possible—but highly improbable. To reverse entropy would be like going back in time. Statistically non-zero, he mumbles, but so unlikely that it’s never been observed. Yet . He adds the “yet” to the end of his sentence, but Katsuki knows it doesn’t mean shit.
“The world is ending,” Izuku mutters to himself. The sharp contours of his spine are made visible when he hunches over the computer. Layers of thermal underwear and sweaters hide the deep ridges of his collarbones. His nails are bitten down to the quick, fingertips pink from the chewing and from the persistent chill inside. His fingers fly over the keyboard in bursts of muted taps, scrambling to keep up with his thoughts.
He mutters the same phrase over and over, checking and re-checking his work, running in circles in the race against entropy. He tries to make heads and tails of the research that Yagi has left behind. Once considered luminaries in their field, Izuku now treads blindly by himself into the dark and unprecedented future that awaits the world.
He scrapes every last piece of data from his mentor’s life and builds an artificial intelligence system from it. It’s nothing but a hollow vestige of the man that was, equipped with a tinny voice speaking in stilted cadences. Nonetheless, Izuku has to try.
He asks Yagi how—if—it can be done. If they can reverse it. Yagi sputters and churns for a moment, sometimes many moments, and comes back with the same response every time: “INSUFFICIENT DATA FOR A MEANINGFUL ANSWER.” It takes another beat before he smiles and says, “I will be here, until I find your answer!”
Izuku spends his days mostly seated in one place, grinding away like Sisyphus in the war against entropy, shouldering this unfair punishment for the world while he lets everything else fall apart around him. There’s nothing Katsuki can do to help but to try and pick up the pieces.
He takes the cold coffee from Izuku’s desk, throwing it back and grimacing when the sludge that had settled at the bottom hits his throat. They’re told that they can’t afford to waste anything anymore. There’s a bitterness at the back of his throat and in his mind when Katsuki thinks that he doesn’t give a fuck about that and heats some water to make more for Izuku. A new cup, piping hot, comes back silently to his desk. Katsuki only gives him a gentle squeeze on his arm, reminding him to at least have a few sips before it gets cold again. Izuku obliges with a quiet thank you and returns to his work without another glance or word for Katsuki. He’s long stopped feeling guilty about it.
Katsuki puts food in front of Izuku like clockwork, sometimes even unwrapping the foil packaging of the calorie bar for him and shoving it into his hand. Izuku’s long stopped resisting it. He takes large bites of the bar while his eyes remain on his work. The gauntness of his cheeks and under his eyes are made all the more hollow by the harsh and unnatural glow of the computer screen. He can’t work if he’s dead; he’s no use to the world if he’s dead. Katsuki hurries to sweep up the crumbs and gather the discarded wrappers around his workstation when Izuku takes the rare bathroom break.
Entropy is the measure of disorder in a system. Left unchecked, energy disperses and the universe tends towards chaos, Izuku explained, as the two of them laid on the floor of his dorm room. Katsuki snorted and asked if that was why his room was such a fucking mess. Izuku laughed and said, “If that will get me off the hook, then yes.” Katsuki’s long stopped finding it endearing, and instead swallows down resentment as he collects dirty clothes and blankets from every corner of their apartment. Izuku fights entropy for the world and Katsuki is left here fighting on his own.
“The world is ending!” Izuku yells, hands raised in frustration. “It’s ending, and you think cleaning up some papers is more important right now?”
It’s not just some papers to Katsuki. It’s a reminder that the man he loves is so hopelessly dedicated to a losing cause. It’s a reminder of the things he can’t control. It’s a reminder of the inevitable end.
He feels like he’s already lost Izuku.
He takes the stack of papers and throws it into the air between them. Between the gaps of the pages fluttering down, Katsuki can see fragments of Izuku’s face—a clenched jaw, a furrowed brow, lips pressed tightly together. For a fleeting moment, he thinks he sees glassy green eyes, but it’s gone as soon as the next sheet of paper flies over it.
He meets Izuku’s eyes again and mirrors his with the same hard and narrowed stare.
“Better?” He hisses. “Maybe you’ll find the answer in this chaos.”
There’s nowhere to go in that small space of theirs, but when they fight, they know where not to go until one of them is ready. Of all the statistical probabilities of different sleeping arrangements in the apartment, they always end up back in the same bed.
The heat of their bodies against each other feels like a rebellion against the decline of the universe. They shed layers of clothing and throw them around the apartment, shivering at the cold air prickling their skin. Katsuki fights against entropy with fevered kisses and the bruising grip of his hands, leaving scorches on Izuku’s skin that dissipate as quickly as they land. Every movement, every gasp and moan that Katsuki pulls out of him is energy lost to the air between them—a petty and selfish victory against the world.
This is the only way he wants to see Izuku fall apart, to come undone in his arms where all the pieces can be kept safe.
“World’s fucking ending, Izuku,” Katsuki grumbles as he turns the faucet to hot and pulls Izuku into the stream of water. “It’s technically one shower if you come in, too.” Katsuki knows he’s wrong, but Izuku knows he’s right.
He doesn’t stop Katsuki when he feels his fingers slow and linger in his soapy hair; he only leans further into him with a deep sigh. For a moment, he can stop thinking about the entropy present in everything they do, down to the rising steam in the shower they stand in. In this moment, Izuku feels suspended in time, all the parts of him held together by Katsuki.
The cold wakes Izuku in the morning. He’s used to Katsuki tucking the blankets tightly back around him when he gets out of bed, but it’s one of those mornings where Katsuki wakes up tired and he lets entropy win a little.
It only takes a couple glances around the apartment for Izuku to guess that Katsuki had gone outside. Going outside was not advised, to say the least, but that’s never stopped him. He’s careful to dress properly and return before too long. Izuku does the same, feeling the pull towards Katsuki stronger than the one calling him to work today.
The world outside sleeps still under a blanket of snow. Whatever wildlife that would have been able to survive the low temperatures could not survive the death of every other resource around them. The only visible evidence of life are Katsuki’s footprints, freshly stomped and leading out towards what used to be a little thicket of trees.
Izuku is almost thankful that the wind barely picked up these days; it’s cold enough without. Without the heat of the sun, air currents rolled in lazily, barely ghosting over the landscape and leaving it mostly untouched. He can still see older sets of footprints, ever so slightly shallower than the ones from this morning. He lets out a puff of hot air, delighting for a moment in the little cloud it forms in front of him before burying his face into his scarf again to conserve his body heat. He quiets the guilt in his head and continues on, measured breaths keeping in time with the crunch of his boots in the snow.
He finds Katsuki not too far out, a baggy silhouette of mismatched outerwear in the distance amongst tall wiry trees. They’re little more than decaying vessels for the water stored inside now, long frozen and half-snapped from the expanding ice. Izuku watches Katsuki kick at them, sending ice crystals shimmering over his head with every thud of his heavy boots. Puffs of hot air mark his growls, punctuating each kick and shower of ice—energy thrown back out into the universe that they would never get back.
If Katsuki was going to lose to entropy, he was going to do it his way.
Katsuki notices that the apartment is tidier when he gets back; their shoes are neatly lined at the door and the counters are clear. Izuku pushes the hat off his head, weaving his fingers through his hair and gently untangling the parts that have frozen together. He brushes away the frost on Katsuki’s brow and runs his hands over his cheeks and ears, until the traces of the biting cold fade from his face. Katsuki sighs and closes his eyes as Izuku’s fingers trace a familiar path from his brow down his jawline. He takes Izuku’s hand into his own and presses his cheek against it, tilting his head ever so slightly to meet Izuku’s lips at the corner of his own.
Izuku lingers there for a moment, their warm breaths intermingling as he murmurs, “Made you coffee. It’s still hot.”
Blond lashes flutter open and Katsuki searches his face, soft gaze shifting into concern. The beginnings of a frown form around the corners of his mouth and crease his brow.
Izuku’s heart aches when the first thing Katsuki asks is, “Is something wrong?”
Izuku shakes his head. Nothing was wrong, but it wasn’t all right either. Nothing had changed the end that they faced, but nothing between them had stayed the same because of him.
“World’s ending, Katsuki,” Izuku settles on a quip, feeling full of emotions but unable to find the right way to start. “Hot coffee is one of the few things that are still right.” He pushes the mug towards Katsuki.
“This coffee’s shit, you know that right?”
“It’s the best I can give you.” Izuku tries to joke back, but his voice wavers.
Katsuki reaches for Izuku, cradling his face as he tries to blink away the tears threatening to fall. Izuku’s face burns under his fingers, still icy and stiff. He runs them carefully over the same path that Izuku’s fingers took, soft and slow down the line of his jaw, clenched from holding back his tears.
A pained gasp escapes from Izuku when Katsuki leans in to kiss the corner of his mouth. It’s okay, it’s okay, he whispers into Izuku’s hair, holding him tight and repeating the words like an incantation that would keep him from breaking.
But when he does, Katsuki is always there to put him back together. It’s the only fight against entropy that he knows how to win. Izuku chokes on his words, mumbling “sorrys” and “I love yous” into the crook of his neck; the rest is lost to the space there when he presses his face in. He doesn’t need the rest of it.
He just needs Izuku whole.
He just needs Izuku with him.
“What’s the fucking point then?” Katsuki shouted at the ceiling of Izuku’s dorm room, raising and dropping his hands in a gesture of exasperation. “What’s the point if everything is constantly falling apart?” He ran his hands through his hair and laced them behind his head, letting out a deep sigh that rolled into a low grumble.
“There isn’t, I guess.”
Izuku looked over at Katsuki, eyes glazed over in existential dread, no longer bothered by his messy room. This revelation made cleaning seem like a moot point to Katsuki.
“We’ll all eventually be stardust,” Izuku says with an airy voice, waving his fingers above them.
Katsuki snorted and slapped his hands away. “Cheesy as fuck.”
“I know,” Izuku chuckled.
They laid there in silence. Izuku fiddled with the strings of his hoodie and Katsuki bore holes into the ceiling, sending his rage up at the sky—in the general direction of the universe.
“But, mm,” Izuku mused as he pushed himself up onto an elbow. “You know what quantum entanglement is?”
Katsuki rolled his eyes. “‘Course I don’t, I’m not a nerd.”
They snapped to Izuku’s when he felt his hand on his chest. Izuku drew diagrams lazily with a finger as he explained. “When two particles are entangled, they stay connected, regardless of the distance that separates them.”
Katsuki closed his eyes, grunting a vague sound of approval for Izuku to continue.
“It’s a phenomenon where any actions performed on one particle...” Izuku’s hand hovered over Katsuki’s face, gently tracing the ridge of his brow, sweeping around to follow his jawline down to his chin. He brought his face close to Katsuki’s, his voice a quiet murmur as he continued, “...will affect the other one, no matter what.”
Izuku pressed a soft kiss onto the corner of Katsuki’s lips, smiling when Katsuki turned to gaze at him with half-lidded eyes. They widened as Katsuki processed the meaning of Izuku’s statement—a hopeful declaration in the face of their transient existence.
“So what you’re saying is,”—Katsuki tugged at the strings of Izuku’s hoodie to pull him close—“I’m never gonna get rid of you.” He reached up with his other hand, mirroring the same lines over Izuku’s face before settling on his nape to bring him close. He kissed the corner of his lips and pulled away, just enough to see his smirk reflected in Izuku’s eyes.
Katsuki watched himself disappear as Izuku grinned, green eyes crinkling into tiny half moons.
“Mmhm. Even after the world ends.”