Work Text:
The thought is first planted in Izuku’s mind in the most asinine way possible.
He arrives back at the agency dorm after a long shift, with barely the energy to get ready for bed before collapsing into unconsciousness. The only thing keeping him awake are the videos he’s scrolling through, just short little clips of cute animals and hero news and fun facts.
When he gets to a video where a man in a lab coat talks about the taste of different compounds, mentioning that nitroglycerin is sweet, Izuku doesn’t think much of it. It’s the last video he watches, and it loops back to the beginning again as Izuku spits out his toothpaste. He wipes his mouth, then grabs his phone, cutting the man off mid-sentence on the word “sweet”.
He yawns wide on his way back to his room, plugging his phone in and collapsing onto his bed face-first, and before long, he’s unconscious.
***
That night he dreams about sucking Katsuki’s dick.
They’re in the arena from the sports festivals. Present Mic’s familiar voice announces the rules of this particular game: first to come loses. Deku doesn’t even register the ridiculousness of the game, too dead-set on winning.
Before he knows it, he’s on his knees, and Present Mic’s cheeky voice is reminding them that Katsuki “sweats a nitroglycerin-like substance, so don’t be surprised if he tastes way sweeter than he acts.”
When he comes, it tastes like icing.
***
Izuku wakes hard and aching, the events of his dream still vivid in his mind. He’s had years of experience with sex dreams about Katsuki, and he doesn’t hesitate to replay the odd events in his mind as he shoves his hand down his boxers and finishes what the dream started.
It doesn’t fully strike him how ridiculous it all was until he’s washing his hands. Of course Katsuki’s come wouldn’t taste sweet, only his sweat contains the nitroglycerin-like compound, and it’s probably only produced in his hands, since that’s where his explosions come from.
Even then, his sweat is only nitroglycerin- like . It’s not fully identical. Would his sweat be sweet?
All through his day, the question haunts him. He’s usually fully focused on his hero work, despite how easily it comes to him now that he’s unlocked OFA’s full capabilities, but he finds himself lost in thought—so much so that he can’t even seem to finish his paperwork for the day, and Shoto sends him upstairs with a shake of his head and a promise to do it for him.
Frazzled and still fixated on this stupid question, he resolves to just get it answered and off his mind. His first thought is to go straight to the source, but he blanches as soon as it crosses his mind. Right, just ask Katsuki what his sweat tastes like, that would go over swimmingly . He grimaces to himself. No, he needs to be more subtle. Preferably, he needs not to bring Katsuki into this at all.
That line of thought is exactly how he finds himself in the support labs, leaning over the counter and trying to sweet-talk the intern into handing over privileged information about Katsuki’s quirk.
“I’m sorry, sir,” she stammers, “but I’m not allowed to share that information with anyone that Bakugou-san hasn’t explicitly authorized.”
“Okay,” Izuku sighs, “that’s fine, I figured it was a long shot anyway. But, look, do you know what part of nitroglycerin makes it taste sweet?”
“I’m… sorry?” the intern asks, clearly baffled.
“Never mind,” Izuku says. Deciding to cut his losses, he backs out of the lab. “Thanks for all your help!” Then he turns on his heel and beats a hasty retreat.
***
Okay, so that didn’t go so well. If he can’t get the information from the labs, that just leaves Katsuki, but it’s 2am at this point, and the chances of him being asleep are very high. Still, Deku is curious, and he figures Katsuki can answer in the morning, so he shoots off a text asking about the chemical makeup of his sweat.
After that, he tries to forget his taste-related fixation and go about his night as normal.
Halfway through brushing his teeth, he breaks. He pulls his phone out and begins to google, settling in for a long, long night. It’s his day off, it’ll be fine.
***
Six hours later, he emerges from his research stupor to use the restroom, and checks his phone, hoping that Katsuki responded while he was distracted.
He pulls up their conversation, and sighs as soon as he sees it, the little “read” glaring beneath his text. Katsuki must have been too busy getting ready for work to respond. He eyes his research longingly.
Just a bit longer, then he’ll go to sleep.
***
The door to their dorm slams shut, startling Izuku badly enough to send sheets of notes fluttering off the coffee table.
Katsuki pushes his mask up into his hairline, revealing his black eye makeup—smudged just a bit at the corners, but mostly intact. There’s a baffled expression on his face as he takes in the sight around him. “What the fuck are you doing in here?”
Izuku perks up. He’s so tired he can feel the bags under his eyes, and he just wants the answer to his question so he can go to sleep in peace. He kind of lost the plot of this whole thing during his frantic research, but he doesn’t need any of this chemistry information, not when he can get his answer straight from the source.
Katsuki removes his support gear, placing it in the bin they keep by the doorway for easy access in case of an emergency, and Izuku watches with hungry eyes as he removes his gloves. “Let me taste your sweat,” he blurts, ever tactful.
Katsuki’s eyebrows shoot up into his hairline. “What,” he asks, “the everloving fuck are you on right now?”
Izuku hums. “Zero hours of sleep and—” He points to the can of energy drink on the coffee table. “—one of those.” He turns back to Katsuki. “Please? I can drink it out of the gauntlets.”
“Fuck no,” Katsuki says, “who knows what would happen if you drank too much of that shit. I don’t want you to fucking die.”
“Aww,” Izuku says, “that’s touching. A bit counterintuitive to my goals at the moment, but touching.”
Katsuki scoffs, his eyes sweeping over the mess in the room. “The fuck, Deku? Is all of this seriously about what my sweat tastes like?”
“Yes,” Izuku groans, “I saw a video about how nitroglycerin tastes sweet and I started wondering if that meant your sweat would taste sweet, and then—” He gestures around the room. “—this happened.”
Katsuki squints at him. “And when’s the last time you slept?”
“Uhhh.” Izuku looks at the clock, then does the mental math. “Maybe… twenty… nine hours ago?”
“Jesus, Deku,” Katsuki groans. “I thought you said you’d cap at twenty-four hours after the clown incident.”
Deku winces. Katsuki is right. The clowns hadn’t been worth it, and this probably wasn’t either.
“Look,” Katsuki says, “if I agree to let you lick my hand, will you go to sleep after?”
Izuku nods furiously, eyes wide and locked in on Katsuki’s hand.
Katsuki warily steps forward, lifting his hand over the back of the couch and offering it with the air of someone who’s trying to pet a rabid dog. Izuku leans forward, taking Katsuki’s offered hand by the wrist. He sticks his tongue out, pressing two of Katsuki’s fingers against it.
Instantly, the sweet taste blooms across his tongue . He doesn’t even think about what he does next, too caught up in the thrill of discovery as he closes his mouth around the fingers and sucks, humming in pleasant surprise.
He chases the taste with his tongue, trying to unpack it. There are layers to it, sweet, but almost spicy; it burns across his tongue in a way he doesn’t associate with sweetness. The taste is starting to fade, so he worms his tongue in between the webbing of Katsuki’s fingers, then pops them out of his mouth, licking down Katsuki’s palm, lapping up the burning, sugary sweetness.
Katsuki makes a soft noise and Izuku halts, suddenly remembering himself. He looks up, and sees a dusting of red splashed over Katsuki’s cheeks.
His tongue retracts back into his mouth, inadvertently licking along the top of Katsuki’s palm as it goes.
Katsuki squirms minutely, and Izuku’s eyes trail down, widening at what they find. He’s almost inclined to believe he’s imagining it but, no, he blinks and it’s still there—a visible bulge in Katsuki’s uniform pants, which was not there when they began.
He looks back up at Katsuki’s face. He looks mortified. His mouth opens to speak, and he begins to tug his hand back. Izuku can tell that he’s about to try to play this off, to put an end to whatever this is, but Izuku doesn’t want it to end. So, he blurts the first thing that comes to mind.
“Do you want my help with that?” He nods down to Katsuki’s crotch.
Katsuki’s lips part further, and a surprised breath gusts out from between them. That’s not a no, but maybe he wasn’t being clear enough. “You know,” he elaborates, “like—” He makes a gesture like he’s jacking off an air penis.
Probably not his smoothest proposition, but he’s kind of running on empty at the moment.
“Are you serious?” Katsuki asks.
“Yes,” Izuku says, nodding earnestly. “Super serious. Look—” He reaches out with Black Whip, stretching it past his bedroom door, feeling his way up to his bedside table, grabbing the lube from the top drawer, then reeling it into his open palm.
Katsuki’s eyes widen. “What, you want to finger me?”
“Oh,” Izuku looks at the lube, “well, I was going to use it to jerk you off, but…” He looks up at Katsuki. “I can do that, too, if you want.”
Katsuki chews his lip, eyeing the lube and Izuku’s fingers in contemplation. “Yeah,” he says. “Okay.”
“Okay, you want me to finger you?” Izuku asks.
A blush spreads over Katsuki’s cheeks, but he nods. “Fuckin’, yeah, that’s what I said.”
“Awesome!” Deku responds, “come here.” He gestures Katsuki over.
Katsuki comes, pulling his shirt up over his head, then steadily removing the rest of his uniform as he goes, until he’s beautifully, gloriously naked and sitting on the couch. Izuku wasn’t expecting the sudden and complete nudity, but he isn’t complaining. The sight of Katsuki, hard and confident and splayed out, wearing nothing but the mask still pushed up to his hairline, stops him in his tracks. He has to spend a moment just taking him in.
Katsuki raises a single eyebrow. “Well?” There’s still a blush high on his cheeks, but it’s fading quickly, and he seems to be determined to ignore any lingering embarrassment.
“Sorry, just, you look really good like this,” Izuku says, uncapping the lube and spreading some over his fingers.
Katsuki smirks. “I know.”
A thrill sparks in Izuku’s gut. God, he loves that confidence. He sets the lube aside, leaning down to take Katsuki’s cock in one hand and bring the fingers of his other to circle at Katsuki’s rim. He bites his lip, looking up at Katsuki. “Can I suck your dick?”
“Yeah,” Katsuki says, a bit breathlessly, “duh.”
His dick tastes nothing like it did in Izuku’s dream. It’s still perfect. Izuku slowly takes it into his mouth, as far as he can without hitting his throat, just to get it wet more than anything, and slides his middle finger into Katsuki’s ass. He rests the knuckles of his pointer and ring finger against Katsuki’s entrance and brings the tip of his thumb between the two to tease at the rim. Katsuki inhales a sharp, shuddery breath, and Izuku bobs his head up, sucking as he goes.
“Fuck,” Katsuki breathes. “More.”
Izuku pulls off his dick with a pop, still slowly thrusting a single finger in Katsuki’s ass. He grabs Katsuki’s dick in his other hand and gives it a single stroke before using the pad of his thumb to toy at the underside. “More what?” he asks, as much to tease as to get clarification.
“Harder, faster, more fingers, all of the a-fucking-bove,” Katsuki demands.
Izuku smiles. “I think I can make that happen.”
He slides his mouth back down on Katsuki’s cock and slowly works his ring finger in alongside his middle. He bobs his head up and down Katsuki’s dick faster, sucks him harder, and once both fingers have been worked inside his ass, he presses the pads up and rubs them along the inner walls of Katsuki’s body. He gets lost in the rhythm of it, barely noticing his own erection as he focuses on Katsuki’s pleasure.
Katsuki sounds so lovely, his moans breathless and genuine. When Izuku looks up at him, he’s gripping the top of the couch, his back arched as he presses himself into Izuku’s touch. He breathes out, and opens his eyes, half-lidded, to meet Izuku’s. “You should fuck me.”
An electric shock of arousal zings in Izuku’s body. He pulls off Katsuki’s dick. “Am I not already?”
“Deku, if you don’t put your dick inside me right the fuck now, I swear to god—“
“Okay, okay,” Izuku laughs, gently removing his fingers from Katsuki’s ass and standing to pull off his pants.
“Shirt, too,” Katsuki says.
Izuku dutifully pulls it over his head, and Katsuki’s eyes rake appreciatively over his body.
Izuku grabs the lube, spreading some over his cock, then lowering himself to his knees. He grabs Katsuki’s hips, pulling him to the edge of the couch. Pressing Katsuki’s legs up and together, he tosses them over his shoulder and holds them to his chest with one hand. He uses the other to grip his cock, leading it towards Katsuki’s entrance. “You ready?”
“Yeah,” Katsuki says, “c’mon, just fuck me.”
So Izuku presses inside, rolling his hips until his cock is buried all the way to the hilt. “God,” he breathes, “you feel so good.”
Katsuki moans, tossing his head back and grabbing a handful of the couch. “Come on Deku, fuck me hard.”
Deku bites his lip, holding Katsuki’s legs in place with one hand and holding one of Katsuki’s ass cheeks with the other, spreading him open and watching him take his cock so nicely, even as he picks up the pace, fucking him harder.
When he looks up to check Katsuki’s face, he sees his lips are parted in a silent ‘o’, his eyes shut tight, brows drawn to the middle. The force of Izuku’s thrusts are rocking Katsuki’s entire body back and forth, and his head is rubbing against the back of the couch, rucking the mask further up on one side and down on the other. Izuku leans forward, bending Katsuki’s legs up towards his chest as he reaches to readjust the mask, and Katsuki gasps, his eyes flying open.
Izuku smiles at him as he pulls his mask down until it’s around his neck, then uses it to pull Katsuki forward into a kiss. Katsuki moans into his mouth, reciprocating the kiss with enthusiasm.
Izuku doesn’t want to stop kissing him, but this angle isn’t great for fucking, and that takes precedence at the moment. He pulls back, noting with some satisfaction that Katsuki’s eye makeup is smearing further now.
“God, you’re so pretty,” he sighs, rubbing his thumb over the corner of Katsuki’s eye and smudging his makeup even more. He loves Katsuki like this, all messy, his lips slick and shining from saliva, his face twisted in pleasure.
Katsuki brings a hand up, and Izuku grabs it, drawing Katsuki’s fingers into his mouth as he thrusts into him again.
Katsuki moans, the loudest he has thus far, and Izuku’s eyebrows raise. Maybe Katsuki’s fingers are more sensitive than he thought. Testing the theory, Izuku licks between the webbing of Katsuki’s fingers, still thrusting, watching his face as he does. Katsuki’s brow furrows, and he whines, his fingers twitching.
Fascinated, Izuku takes it further, fucking him harder, while teasing gentle, feather-light swipes of his tongue over the palm of Katsuki’s hand.
Katsuki tastes so sweet, he looks so good, he sounds amazing, god, he’s fantastic. He’s making these sharp little moans to the beat of Izuku’s thrusts, and his stomach and fingers are twitching, and he’s twisting his hips, and as Izuku watches, enthralled, a tear leaks out of his eye, taking a line of his already-messy black makeup with it.
Izuku stops teasing him, leaning back a bit and pressing Katsuki’s hand closed, laying an apologetic kiss against his knuckles.
Katsuki’s legs begin to slide off his shoulders, and he lets it happen, gently readjusting Katsuki so his hips are twisted to the side, his legs resting on the couch now. He smiles down at Katsuki, just holding his hand and watching his face as he takes him so well, clearly loving it.
Then he drops Katsuki’s hand. “Touch yourself,” he says, “I want to see you come.”
Katsuki, seeming to forget his habitual obstinance, immediately drops his saliva-slick hand to his cock, spreading his legs for easier access and nearly kicking Izuku in the face in his haste.
Izuku watches his hand move over his cock, doing his best to match the hurried pace with his thrusts. He watches Katsuki take his dick, then watches his face contorting in pleasure, then watches as he comes, hard and messy, all over his own stomach. Izuku doesn’t slow down, can’t bear to, not with the way his own orgasm is building low in his gut. His muscles are tensed and ready to release, if only he can fuck Katsuki a little harder, a little faster, until he pushes himself to the edge.
Finally, gloriously, he comes, burying his cock to the hilt in Katsuki’s ass and releasing inside him. His cock pulses with it, singing with satisfaction at the tight heat around it.
Izuku gives a few more soft, gentle thrusts, then eases himself out of Katsuki’s ass. A bead of cum rolls out in his wake.
He bites his lip. “Sorry, I forgot to ask if I could come inside.”
Katsuki shakes his head. “Don’t fucking apologize, that felt fucking amazing.” He stretches his limbs out, sighing in contentment. “We should do it again sometime.”
Izuku laughs affectionately. “Yeah, we definitely should.”