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Izuku groans softly as he comes to, opening his eyes slowly. His body aches, but all his limbs seem to be intact. He can hear grumbling coming from beside him, so the impact of the spell going wrong must not have done too much damage to them. He sits up to take stock of his lab and pauses as he brings a hand to his throbbing head.
That's not his hand.
Large and strong, soft despite their calluses and otherwise unblemished—such a big contrast to his own scarred hands. Izuku has dreamed of these hands since he was a young child, chasing after them and their owner for as long as he can remember. He has ached to hold them, to have them reach back and take his own in a grip he knows would be gentle.
Izuku would know these hands anywhere, but they don't belong to him. They belong to—
"Fuckin' hell," groans his companion, and Izuku stiffens. "What the fuck was that spell, you idiot? Wait, what the—"
Izuku wants to cry. Looking back at him is his own face, twisted in an expression he's never seen on it before: furrowed brows and a sneer curling his usually smiling mouth. The green eyes he's been told are big and bright are narrowed as they stare back at him, like someone else is behind them. Which means—
"Oh, gods," he says, and that's not his voice. It's too deep, too rough as it rasps off his tongue. It doesn't send shivers up his spine hearing it with these ears, either, and that has panic building up in his chest. "Oh gods, oh gods, I—Oh, gods..."
A strange warmth builds along with the panic, a heat concentrated behind his ribs that climbs as his breathing becomes erratic. He's starting to hyperventilate, he knows exactly what's happening, but he can't seem to remember the exercises that help him calm down. The heat in his chest is burning now, hotter and hotter, and oh, gods, what's happening to me—
"Oi, Deku! Hey!"
Hands land on his shoulders—they're too small, he's too broad—trying to ground him. Hearing his own voice come out so harsh only adds to his hysteria. Izuku barely feels the tears trailing down his cheeks; he only realizes he's started crying when thumbs brush them away.
"Izuku," Katsuki says with Izuku's voice, softer but just as commanding. Izuku fights to meet his gaze—wrong wrong wrong. "Izuku, you need to calm down or you're going to fry us both. Dragonfire reacts to your emotions if you can't control it. Breathe, Izuku. Listen to me, and breathe."
Izuku does as Katsuki tells him and inhales deeply, drawing as much air into his lungs around the burning heat of the dragonfire building inside him as he can. He exhales and repeats, until the heat starts abating. His eyes fall closed at some point, and he finally picks out the cool, sweet scent of mint and pine. Immediately his body—Kacchan's body—relaxes, the tension tightening his limbs bleeding out until he's practically slumped over. A soft rumble starts up, and Izuku can't pinpoint what it is until he realizes it's coming from him.
He's only heard Katsuki purr a couple of times, and each time was by complete accident—stumbling upon him during quiet moments where Katsuki had been alone and let his guard down.
"There we go," Katsuki murmurs. It's so strange to hear him speaking with Izuku's voice. "Just like that, sweetheart. You're doing good. Keep breathin' for me."
The purring continues as his eyes flutter back open once the dragonfire's heat has completely gone away. Izuku feels calm again, almost sleepy. The mint and pine is comforting, and the warmth suffusing his chest is soothing instead of frightening. Familiar, almost. He nuzzles against the source of the scent, startling only slightly when it moves against his cheek and he realizes Katsuki is holding his wrist to his face.
Izuku vaguely recalls a lesson on the scenting habits of dragonborn and how they'll rub the glands in their wrists and necks together in order to transfer scents onto others. He figures that's what this is now.
"Mm, thanks Kacchan," he mumbles back. It's still strange to hear Katsuki's voice when he expects his own. "How did you know that would help? The scent thing, I mean."
Katsuki gives him a look like he can't believe Izuku is forcing him to explain things. It's a look Izuku sees often and it makes something in his chest flutter in a way that's familiar and foreign at the same time. A feeling he knows, but can't quite decipher.
"I like to think I know myself pretty well, idiot," he says while rolling his eyes. His words are haughty, but his tone is strangely gentle. "I might be in your body right now, but I still know how mine works."
Izuku thinks about that. His thoughts feel sluggish, slower to draw conclusions than he's used to, and he finds it oddly fascinating to think it's because it's Katsuki's brain he's using. So interesting!
"So..." he muses, still absently nuzzling against Katsuki's wrist—his own wrist, actually, and that's kind of weird to think about, so he doesn't. "My scent calms you down? Why?"
Katsuki watches him silently for a moment. Izuku feels that familiar-foreign flutter in his chest again as he looks into green eyes, and he wonders why Katsuki's body has that kind of reaction when he looks at Izuku. What could it be? Why does it feel like Izuku should know—
With a soft huff, Katsuki ruffles Izuku's hair and stands up. "Don't worry about it, nerd. Let's just concentrate on fixing this fuck-up of yours. I can feel your magic buzzing under my skin and it's gonna drive me fuckin' insane."
"Ah—yeah!"
Izuku hurries to his feet, wobbling only slightly when his center of gravity isn't quite what he's used to—and also he's much taller than normal. He has to look down to meet Katsuki's gaze right now, and he's not sure he's a fan of it. There's also an odd weight on his head, and—oh. Katsuki's horns.
Very strange, indeed.
"Well, Kacchan," he starts, looking around at his lab finally, now that he's no longer quite as panicked about the fact that he and Katsuki have switched bodies. "I should have most of the ingredients for the counter-spell, but I know there's at least one thing that we'll have to travel to get. And you'll probably have to do most of it, since you have my energy signature right now—you said you could feel it, right? I can definitely feel yours, now that I'm concentrating. It's very warm, actually. I can see why you don't like wearing a lot of layers—"
"Deku," Katsuki interrupts him. He looks like he's trying to fight a grin. There's a pretty flush to his cheeks, nearly swallowing the freckles, and Izuku finds himself feeling weak in the knees at the sight of it. "Just tell me what we need to get and how to put it together. You can dissect this as we move."
Izuku shakes himself from the stupor, feeling his own cheeks heating up. "R-Right."
It hits him, then, that he's going to be spending an undetermined amount of time in the body of his best friend and the man he's secretly in love with. And said best friend and secret love is going to spend that same amount of time in his body, which—if the things he's experiencing are anything to go by—will be reacting to Katsuki's body in the way Izuku normally would. Which is to say: like a pining, longing fool.
Great. Fantastic.
It's going to be a long few days in their immediate future.