Archive of Our Own

The training ground smelled like scorched grass and ozone, that particular sharp tang Izuku had learned to associate with Katsuki going all out. Around them, Class 1-A had arranged themselves in the loose semicircle they always fell into during these matches, half paying attention, half pretending not to be riveted.

Izuku ducked under a blast that singed the air where his head had been a half-second before, his ears ringing faintly with the aftershock of it. He rolled, came up on the balls of his feet, already tracking Katsuki’s next movement before his own balance had fully settled.

“Slow,” Katsuki called, grinning with too many teeth. “You’re getting slow, Deku!”

He wasn’t, and Izuku knew perfectly well he wasn’t, no matter how much Katsuki liked to bait him with it mid-fight. There was a rhythm to sparring with Katsuki that had very little to do with winning, something that lived in the space between what Katsuki said and what his body actually did, a language they’d built slowly over years of watching each other fight. Izuku read the drop of Katsuki’s shoulder a fraction of a second before the explosion came, already moving when it did, angling his body so the heat only grazed his side instead of catching him full on.

His mind ran through the calculations without asking permission, measuring distance and trajectory while cataloguing the way Katsuki had started favoring his right after twelve minutes of continuous sparring, along with the tiny shift in his stance that usually meant he was committing to an attack rather than a feint. Izuku had a notebook full of this kind of thing back in his dorm room, dog-eared, covered in his own increasingly illegible handwriting, but by now most of it lived in his muscles rather than on the page.

He needed an angle. Katsuki was pressing forward again, relentless, and Izuku’s usual approach, full-body redirection, One For All humming warm under his skin, would leave him too exposed on the follow-through. He thought of Blackwhip instead. A quick loop around, come at him from the side he wasn’t watching.

He reached for the quirk the way he always did, expecting the familiar tug of black tendrils answering his call, that familiar sense of intent catching somewhere deep inside him before the quirk answered.

Instead, something happened that shouldn’t have been possible, something so completely outside the rhythm he’d learned with Blackwhip that every instinct he’d developed over the years seemed to fail him at once.

One of the tendrils, instead of curling toward open air like he’d told it to, snapped in the opposite direction entirely, whipping across the space between them and winding itself tight around Katsuki’s wrist before Izuku could even register the shift.

For one full second, neither of them moved, the training ground gone strangely quiet around the two of them like the rest of the class had collectively forgotten to breathe.

Izuku stared at his own quirk like it had grown a second head. It wasn’t loose, either; it wasn’t the accidental brush of something half-formed. It had wrapped around Katsuki’s wrist with a kind of purpose, snug enough that he could feel the pulse there, feel the heat still radiating off Katsuki’s skin from the last explosion he’d thrown.

Katsuki had gone still too, mid-lunge, weight balanced on the balls of his feet like his body hadn’t caught up to the fact that his brain had stopped issuing orders. He looked down at the black tendril circling his wrist, then up at Izuku, red eyes narrowed into something that wasn’t quite anger yet, more like disbelief searching for a place to land.

“Oi,” Katsuki said. “What the hell was that?”

“I-” Izuku’s concentration shattered along with his sentence. The tendril dissolved instantly, snapping back into nothing, He flexed his fingers uselessly, staring at them as though they might somehow explain what had just happened. “I don’t know! I didn’t, I wasn’t aiming for you, I swear, I was going for the left side, that’s not even close to-”

“You grabbed my wrist!” Katsuki flexed the hand in question, testing it, though there was nothing left to test. “With your creepy shadow tentacle thing. That doesn’t just happen, Deku!”

“I know! I know it doesn’t, okay? I don’t understand it either. It’s never done that before, not once, not even when I’m distracted or—”

He didn’t get to finish. Katsuki’s stance shifted back into readiness with terrifying speed, an explosion already crackling to life in his palm. “You can apologize later! We’re not done!”

Izuku barely had time to throw himself sideways before the blast tore up the ground where he’d been standing, close enough that he felt it kiss the edge of his jaw. He recovered instinctively, One For All flooding his limbs, and the fight swallowed him whole again: reflex against reflex, attack against counter, the two of them moving through a pattern they’d worn smooth over years of exactly this.

A few minutes later, it ended the way their matches usually did, with Katsuki managing to pin him by such a narrow margin that half the class groaned at how close it had been. Izuku hit the ground on his back, chest heaving, Katsuki’s boot planted lightly beside his ribs in a gesture that was more habit than actual victory pose at this point.

“Dead!” Katsuki announced to no one in particular, already turning to accept the scattered applause with insufferable smugness.

Izuku barely registered it, the applause and Katsuki’s gloating both fading into background noise while he stayed on his back, still staring up at his own hand and turning it over slowly, like it might confess something if he looked at it hard enough.

He hadn’t reached for Katsuki, at least not consciously, and that was the part Izuku couldn’t seem to get past. Blackwhip still surprised him sometimes, even after all this time, but this hadn’t felt like one of those moments when the quirk slipped loose without warning. Something in him had reached without asking, some part of Blackwhip, or maybe some part of him, that operated below the level where he got to make decisions.

It had gone straight for Katsuki instead of the open air where he’d actually aimed it, and instead of anyone else who’d been standing nearby when it happened.

Katsuki, specifically, which left him wondering, uneasily, why it would have been him out of everyone.

Izuku sat up, dust clinging to the back of his shirt, with no answer for why that thought made his stomach do something complicated and entirely unrelated to the fight.

The crowd broke apart as the match officially ended, everyone drifting back toward the equipment shed in loose clusters, and Izuku told himself, quietly, firmly, that it had been nothing. A misfire. Some strange overlap between his focus and his quirk that meant nothing at all.

Class 1-A, unfortunately, had other ideas, and they arrived at his side in a loose, chattering knot before he’d even managed to fully get to his feet.

“Dude.” Kaminari was grinning before he’d even fully closed the distance, electricity still crackling faintly at the ends of his hair from earlier, like he hadn’t quite powered all the way down. “Your quirk just full-on tackled Bakugou. What was that?”

“It wasn’t a tackle,” Izuku said. “It just, it grabbed his wrist. For a second.”

“A romantic second,” Kaminari said, waggling his eyebrows, and Izuku felt his face heat up so fast it was almost embarrassing.

Kirishima laughed, loud and easy, throwing an arm around Kaminari’s shoulders like that might somehow soften the blow. “Seriously though, has your quirk decided Bakugou’s its favorite person? Does Blackwhip have a type now?”

“That isn’t what happened!” Izuku’s hands came up, half defensive, half like he could physically wave the idea away. “Blackwhip does that sometimes, it responds on its own if I’m startled or really focused on something, it’s not, it doesn’t pick favorites-”

“Sounds like it picked one today,” Kirishima said, still grinning, but not unkindly.

Tenya, who’d been standing at the edge of the group with his arms crossed in the particular way that meant he was already three steps into analyzing the problem, adjusted his glasses. “If I may. Did you experience anything unusual immediately before the activation? Any shift in emotional state, or physical sensation?”

Izuku opened his mouth to say no, then actually thought about it, which was somehow worse. “I was concentrating on Kacchan’s movements. Really hard. But that’s not unusual, I always focus that intensely when I’m sparring with him, he moves fast, if I don’t pay attention I get hit.”

“Hm.” Tenya made a small noise that suggested he was filing that away for later, which did nothing for Izuku’s nerves.

Ochako tilted her head, hands laced behind her back. “Has Blackwhip ever grabbed anyone before? Like, without you meaning it to?”

“It’s moved on its own a couple times,” Izuku admitted. “When I’m startled, mostly. But it never went for anyone specifically. It just kind of, flailed. This was different.”

“Different how?” Ochako pressed, leaning in slightly, clearly not willing to let the answer slide by unexamined.

“It went straight for him. Not just, out, not some random direction like it usually does when it slips. For him, specifically, like it knew exactly where he was standing.”

Shoto hadn’t said anything yet. He’d been standing a little apart from the group, arms loose at his sides, watching Katsuki across the training field with an expression that gave away nothing at all. When he finally spoke, his voice was even and quiet enough that the others had to lean in slightly to catch it.

“There were several people closer to you when it happened.”

Izuku blinked, caught off guard by how quietly certain Shoto sounded. “What?”

“When Blackwhip activated. Kirishima was closer. So was Ochako. Even I was closer than Bakugou was.” Shoto’s mismatched eyes flicked to him, unreadable. “It didn’t reach for the nearest person. It went straight to Bakugou.”

Nobody said anything for a second. The observation settled somewhere uncomfortably deep in Izuku’s chest, small enough that he could almost ignore it if he tried, but heavy enough that every attempt to push it away only seemed to make him more aware of it.

“I don’t,” he started, and then didn’t know how to finish that sentence. “I don’t have an explanation for that.”

Kaminari opened his mouth, probably to make another joke, but something in Izuku’s expression must have stopped him. He closed it again instead.

Across the field, Katsuki was toweling off, his sweat-damp hair sticking up in every direction, and even from that distance Izuku could feel the weight of his stare. Not glaring, exactly. Just watching, red eyes fixed on him with an intensity that made Izuku’s stomach twist into something he didn’t have a name for yet.

He looked away first, telling himself it didn’t mean anything, even as some quiet, unhelpful part of him kept replaying the exact moment the tendril had found Katsuki’s wrist, so certain in its movement that it almost seemed as though it had never been looking for anywhere else.

By the time Izuku made it back to his dorm room that evening, the whole thing had settled into his chest like a splinter he couldn’t stop worrying at, small enough to ignore for a few minutes at a time but never quite gone. He dropped his bag by the door, showered, ate dinner without really tasting it, and then sat down at his desk with three different notebooks spread out in front of him like he was preparing for a final exam nobody else knew he was taking.

The first notebook was old, one of his earliest ones from before UA even, filled with cramped handwriting and hastily sketched diagrams from back when he’d still been mapping out theories about quirks that weren’t his own. The second was newer, dedicated almost entirely to One For All, its pages full of percentages and stress calculations and increasingly confident notes about control. The third was the thinnest of the three, reserved for Blackwhip specifically, and it was the one he pulled toward himself first.

He flipped back to the early entries, the ones from right after the quirk had manifested, back when it had felt less like an ability and more like something feral living just under his skin. Strong correlation with emotional state, he’d written back then, underlined twice. Activates most reliably under extreme stress, fear, or protective instinct. Difficult to summon deliberately; comes more easily when triggered by feeling rather than by will.

That much, at least, hadn’t changed. Even after months of training, Blackwhip still responded best when something in him wanted it to, some emotional undercurrent doing half the work his conscious effort was supposed to accomplish on its own.

Which meant something had been happening under the surface today. Some feeling strong enough to override his actual intent and send a tendril somewhere he hadn’t told it to go.

He tapped his pen against the edge of the notebook, staring at the wall like the answer might be written there if he looked hard enough.

He hadn’t been scared. Not really, at least not in the way he usually was before an unplanned activation. He knew Katsuki’s attacks too well for that, could read them coming from a mile away even when they were moving at explosive speed. Startled, maybe, in that split second before he adjusted, but that wasn’t new either. He got startled during sparring matches all the time, and Blackwhip had never once responded by grabbing someone’s wrist, so startle alone couldn’t be the whole answer, could it? Unless there was some threshold he’d never actually tested before, some combination of variables that only lined up under very specific conditions, which would mean he needed a different kind of data than anything he’d collected so far.

Focused, definitely. He’d been tracking Katsuki’s every movement with the kind of intensity that came from years of practice, cataloguing shoulder drops and weight shifts and the particular change in Katsuki’s stance that came right before he committed to an attack, but that level of focus wasn’t new either; he did that every single match, had been doing it since they were kids sparring in empty lots after school, so if focus alone could trigger something like this, it should have happened a hundred times before now, not just once. Excited too, in the particular way he always felt when he was sparring with someone who could actually push him, forcing him to move faster and think sharper than he ever had to with anyone else. And underneath all of that, if he was being completely honest with himself, there had been a low hum of something that might have been nervousness, though he couldn’t say what there had been to be nervous about. He fought Katsuki all the time. There was nothing new about today that should have made his pulse do anything different, unless… he scribbled the thought down before it could slip away, unless something about today specifically had been different in a way he hadn’t consciously registered yet.

None of it seemed unusual enough to explain what had happened. That was the frustrating part. He could list a dozen ordinary explanations, but none of them accounted for a tendril crossing the training ground just to find one person’s wrist when there had been so many others standing nearby.

He wrote them all down anyway. That was what he did when something didn’t make sense: he broke it into pieces small enough to examine individually.

Possible triggers:

1. Heightened focus during sparring (baseline, occurs every match)
2. Startle response to sudden movement (baseline, occurs frequently)
3. Unknown emotional variable, unidentified
4. Coincidence / muscle memory error

He stared at the fourth option the longest. It would be the easiest explanation, certainly the least complicated one, and some small, tired part of him wanted very badly to just accept it and move on. Quirks misfired sometimes. His own control wasn’t perfect, wouldn’t ever be perfect, not with something as unpredictable as Blackwhip layered on top of One For All. Maybe it really had just been an error, a strange one-time glitch with no deeper meaning attached to it.

But he didn’t quite believe that, and he’d learned a long time ago not to ignore the part of himself that knew when an easy answer didn’t quite fit.

He needed data. That was the only way he knew how to actually settle this instead of turning it over in his head all night without getting anywhere. Tomorrow, between classes, he’d test Blackwhip around a few different people, nothing dramatic, just small controlled moments where he let his focus sharpen the way it had during the match and see whether the quirk did anything unexpected. If it behaved normally around everyone else, stayed exactly where he aimed it, then he’d have his answer. The incident with Katsuki would have been a coincidence, an anomaly, nothing worth losing more sleep over.

If it didn’t, well. He’d figure out what came next when he got there.

Izuku closed the notebook, turned off his desk lamp, and lay awake far longer than he wanted to admit, replaying the exact sensation of the tendril snapping toward Katsuki instead of away from him, searching for the feeling that had sent it there and coming up with nothing he could name.

The training room was mostly empty during their free period, save for the four of them and a few stray pieces of equipment shoved against the far wall, and Izuku had never been more grateful for a quiet space in his life. He’d asked Ochako, Tenya, and Shoto the night before, keeping the explanation vague and framing it as a simple control check for Blackwhip’s reliability, and none of them had pressed for more than that, which he appreciated more than he probably let on.

“Okay.” He rolled his shoulders, shook out his hands, and tried to look more confident than he felt. “Ochako first. I’m going to activate Blackwhip and reach for you, and I want you to move unpredictably, like you would if you were surprised or distracted. Just, see how it responds.”

“Got it.” Ochako settled into a loose stance, bouncing lightly on her toes. “Ready whenever.”

He reached for the quirk, felt the familiar tendrils unspool from his forearm, and sent one arcing toward her exactly where he aimed it. Ochako dodged sideways at the last second, and the tendril adjusted smoothly, tracking her the way it was supposed to, responsive and precise and completely, boringly normal.

“Nice,” Ochako said, grinning. “Very tentacle-y. Ten out of ten.”

Tenya went next, standing with his usual rigid posture even as Izuku warned him to move however felt natural. The tendril reached for him with the same clean accuracy, never deviating or pulling in a direction Izuku hadn’t intended. Izuku let it wrap loosely around Tenya’s arm before retracting it, only then realizing he’d been holding his breath as he exhaled.

“Consistent activation,” Tenya noted, adjusting his glasses. “No irregularities that I could observe.”

Shoto’s turn produced the same result. Izuku reached, the tendril responded, wrapped, released, all exactly as intended, and by the time it was over he felt something in his chest loosen that he hadn’t fully realized had been clenched since yesterday.

Maybe it really had been a coincidence. Maybe his mind had built an entire mystery out of one strange, meaningless misfire, the sort of thing that could happen with a quirk as unpredictable as Blackwhip, and he’d simply spent an entire evening turning it over when there had never been anything worth solving in the first place.

He was turning that thought over, letting himself sink into the relief of it, when the training room door opened and Katsuki walked in.

Izuku didn’t even look up at first. He was facing the opposite direction, halfway through telling Ochako that they probably had enough data to call the experiment complete, his attention nowhere near Blackwhip and his hands completely still, when he felt something shift along his forearm.

One of the tendrils lifted from his arm.

He felt it before he saw it, that same strange pull from yesterday, and by the time he turned his head the tendril had already stretched halfway across the room, extending slowly and deliberately toward the exact spot where Katsuki stood in the doorway.

“Wha—” Izuku’s stomach dropped as the tendril continued toward him. He yanked at the quirk with everything he had, forcing it back into himself so fast it stung, and it snapped away and dissolved before it got anywhere close to actually reaching him.

The room had gone very quiet around them, the argument over game rules forgotten entirely in favor of watching whatever this was turning into.

Katsuki, to his credit, hadn’t moved from the doorway, arms crossed, watching the whole thing with an expression Izuku couldn’t quite read, something caught between suspicion and a wariness he was clearly trying not to show.

“That,” Tenya said slowly, “was nearly identical to what happened during your sparring match yesterday. The trajectory was the same, the activation was unprompted, and even the target was identical.”

“It didn’t do that with any of us,” Shoto added, his voice quiet and matter-of-fact in a way that somehow made the observation worse. “Not once.”

Izuku’s face was burning. He didn’t have a response for either of them, mostly because there wasn’t one, not anymore. The pattern was sitting right there in front of all four of them, impossible to explain away.

Ochako hadn’t said anything at all. She was looking at him with an expression that wasn’t quite surprise and wasn’t quite amusement either, something more thoughtful than both, and it made Izuku more nervous than anything Tenya or Shoto had said so far.

“Ochako?” he asked, when the silence had stretched on long enough to feel uncomfortable. “What are you thinking?”

She glanced toward the doorway, where Katsuki hadn’t moved, watching them with that same unreadable expression, then back at Izuku, and whatever she’d been about to say she apparently decided to trade for something simpler instead.

“I think,” she said, “you should keep investigating.”

The pattern, once Izuku started looking for it, turned out to be impossible to unsee.

It happened on Tuesday, when Katsuki walked past his desk on the way to his own seat, close enough that Izuku caught the faint smell of smoke that always clung to him after morning training, and a tendril twitched loose from his sleeve before he’d even registered what it was doing. He shoved it back down so fast his hand cramped, and spent the rest of homeroom pretending to take notes he wasn’t actually writing.

It happened again on Wednesday, when Katsuki called something across the classroom about a group project deadline, his voice loud and irritated in the way it always was, and Izuku felt the quirk stir before he’d even finished speaking, as though Blackwhip had recognized his voice before Izuku’s conscious mind could catch up.

It happened during training, obviously, though by now Izuku had gotten marginally better at catching it before it went anywhere visible, keeping himself in a constant state of vigilance that left him exhausted by the end of every session for reasons that had nothing to do with physical exertion.

And then, on Thursday, it happened before Izuku had even seen him. He was walking down the hallway toward the cafeteria, half listening to Kirishima talk about some new manga he’d started, when Katsuki’s voice carried around the corner ahead of him, sharp and familiar even muffled through the noise of the hallway, and Izuku felt the tendril start to lift from his arm before Katsuki had even come into view.

“Okay, that’s just unfair,” Kirishima said, laughing as Izuku yanked his sleeve down over his wrist like that might physically stop what was happening underneath it. “It knows his voice now? From around a corner?”

“It’s not funny,” Izuku muttered, face hot.

Kirishima held up both hands in mock surrender, though the grin never actually left his face. “It’s a little funny.”

“It’s not, it’s really not. That’s a voice recognition problem now, on top of everything else. That’s an entirely new variable I didn’t even have on my list,” Izuku muttered, mostly to himself, already trying to figure out where exactly he was supposed to put it in his notes.

Every time it happened, the embarrassment hit him just as hard as the first, as though his body hadn’t yet learned that this was a recurring problem and insisted on treating each new incident like a fresh humiliation. It was one thing to have an unpredictable quirk. It was another thing entirely to have one that seemed to have picked a single, very inconvenient target and refused to let go, especially now that half the class had started watching for it whenever Katsuki entered the room.

Tenya, true to form, treated the whole thing like a problem that could be solved if they simply gathered enough information. He sat Izuku down twice that week with actual printed material on emotional regulation techniques, suggesting breathing exercises and visualization methods meant to help stabilize quirk activation during moments of heightened feeling.

“The underlying issue is almost certainly rooted in an unregulated emotional response,” Tenya said, tapping his pen against a diagram that looked suspiciously like a flowchart. “If we can identify and manage the specific trigger, you should be able to regain full conscious control.”

“Right,” Izuku said. “The trigger.”

“Once we isolate what emotional state precedes activation, the solution should become considerably more straightforward.”

Izuku nodded along, took the notes, and tried the breathing exercises that night in his room with limited success. He didn’t mention that he was fairly certain Tenya’s flowchart was missing several crucial branches.

Shoto, meanwhile, offered very little in the way of solutions and considerably more in the way of observations Izuku would have preferred not to hear. He’d taken to watching the incidents with a kind of clinical interest that made Izuku distinctly uncomfortable, like he was cataloguing something rather than simply witnessing it.

“It’s very specific,” he said, after the hallway incident, apropos of nothing, while they were both getting food in the cafeteria line. “Not general anxiety. Not the startle response Tenya keeps describing. It’s specific to him, and nobody else.”

Izuku kept his eyes on his tray, refusing to give Shoto the satisfaction of a reaction. “I know that.”

“I’m just saying it out loud,” Shoto said, sliding a bowl of rice onto his own tray like the observation cost him nothing at all.

“You didn’t have to.”

Shoto shrugged and moved on to pick up a tray like he hadn’t just said the exact thing Izuku had been trying very hard not to think about too directly.

Ochako was the strangest part of all of it, in a way that Izuku couldn’t quite put his finger on. She never joked about it the way Kaminari or Kirishima did, and she never offered theories the way Tenya and Shoto had, even when Izuku was practically begging someone to give him one. She just went quiet every single time it happened, watching with an expression that flickered somewhere between careful and knowing, and said absolutely nothing about it afterward unless Izuku pushed.

He’d started pushing more often than he probably should have.

“You always get this look,” he said to her one afternoon after Blackwhip had drifted a full two feet toward Katsuki’s table before Izuku managed to wrestle it back under control. “Every time. What is it? What are you thinking?”

“Nothing,” Ochako said, entirely too quickly, focusing very intently on her food.

“Ochako.” He said her name flatly, unconvinced, and didn’t look away.

“I just think,” she said carefully, choosing each word as though she were measuring exactly how much she could get away with saying, “that you should keep investigating. On your own. You’ll figure it out.”

“That’s not helping.” He set his chopsticks down, giving up on pretending he was still eating.

“It’s the answer you’re getting.” She finally looked up at him, something stubborn and a little sad flickering behind her eyes before she smoothed it away.

She wouldn’t budge past that, no matter how many different angles he tried over the following days, and the more she refused to say, the more determined Izuku became to find the answer himself, whatever it turned out to be and whatever it might mean once he did.

Aizawa paired them together again during afternoon training, calling out assignments in his usual flat monotone like he had no idea what kind of week Izuku had been having, and the second Izuku heard Katsuki’s name attached to his own, he decided this was going to be the session where he finally got it right.

He’d been thinking about it all morning. If he could just concentrate hard enough, keep Blackwhip on a tight enough leash, and prove to himself that this was a matter of focus and nothing else, then maybe the whole embarrassing mess of the past week would finally start making sense as exactly what he wanted it to be: a fixable problem, solvable through effort, nothing stranger than that.

“You’re doing that stupid look,” Katsuki said, rolling his shoulders as they squared off across the mat.

“What?”

“That constipated overthinking thing. Your face does it.” Katsuki cracked his knuckles, sparks already dancing faintly across his palms. “Just fight normal, Deku.”

Izuku didn’t answer, mostly since he wasn’t sure he could without giving away how much thought had actually gone into this, so he settled into his stance and let the match begin.

It went fine for the first several exchanges. He kept Blackwhip firmly leashed, using it only when he consciously chose to, redirecting his attacks with careful precision instead of the instinctive bursts he usually favored. The problem, no matter how hard he concentrated, was Katsuki himself. Every time Katsuki closed the distance, every time his fist or palm came within a few feet of landing, something in Izuku’s chest tightened, an awareness that had nothing to do with fear and everything to do with something he couldn’t name and definitely couldn’t turn off.

It happened again near the end of the match. Katsuki lunged in close, faster than Izuku had anticipated, and in the same motion threw an explosion off to the side that Izuku hadn’t seen building until it was already too late to dodge on his own. Katsuki’s hand shot out instead, closing hard around Izuku’s wrist, and yanked him sideways out of the blast radius before the heat could catch him.

For half a second, all Izuku could feel was the grip, tight and warm and startlingly steady, along with the strange closeness of Katsuki being right there.

Then, without any warning at all, Blackwhip moved on its own.

A tendril shot from his other arm before he’d registered any conscious decision to summon it, wrapping around Katsuki’s forearm with the same strange certainty as before, snug and immediate.

Katsuki looked down at it, then dragged his gaze back up to Izuku’s face.

Heat rushed across Izuku’s face, equal parts humiliation and panic. “Sorry! Sorry, I’m-” He grabbed at the quirk mentally, trying to force it back, but it resisted for several long, agonizing seconds, curled tight around Katsuki’s arm before finally uncurling and dissolving away.

The silence that followed stretched long enough for Izuku to seriously consider melting into the floor rather than facing Katsuki.

“Has it always been this clingy?” Katsuki asked, flexing his arm like he was checking whether the sensation of it had actually left or just gone temporarily invisible.

“No!” The word came out louder than Izuku meant it to. “It’s never done this before. Not like this, not until this week, I don’t know what’s going on with it, I swear I’m not doing this on purpose.”

Katsuki’s eyes narrowed, studying him with the kind of scrutiny that made Izuku want to physically shrink out of existence, some mixture of suspicion and something else he couldn’t quite place underneath it.

“Figure your shit out, Deku,” Katsuki said finally, low and rough, before turning and walking off toward the water station without waiting for a response.

Izuku stood in the middle of the mat, staring after him, his wrist still faintly warm where Katsuki’s hand had been, and had absolutely no idea how he was supposed to do that.

Ochako found him afterward, sitting cross-legged on the grass at the edge of the training field with his notebook open on his knee, still trying to put words to what had happened with Katsuki’s arm still warm in his memory. She dropped down beside him without asking, close enough that their shoulders nearly touched, and peered over at the page he’d barely started filling.

“Another entry?” she asked.

“Another entry.” He tapped his pen against the margin, staring at the half-written line like it might finish itself if he waited long enough. “I don’t know what to write anymore. It’s the same thing every time. I keep saying it’s emotional, but I still can’t figure out which emotion.”

“What do you think it is?”

“I don’t know.” He rubbed the back of his neck, frustration bleeding into his voice. “I’ve gone through everything. Fear, excitement, focus, none of it fits right. It’s like there’s something specific happening and I just can’t see it clearly enough to name it.”

Ochako pulled her knees up to her chest, wrapping her arms around them, and studied him for a long moment before speaking again. “Can I ask you some questions? Not about the quirk. About Bakugou.”

Izuku blinked, caught off guard by the shift. “Okay?”

“Do you get nervous around him?”

“Yes.” The answer came easily, automatically, before he’d even thought to hesitate over it. “I mean, he’s intense. Being around him kind of always makes my heart rate spike a little.”

“Do you get excited when you train with him?”

“Yeah, obviously. He pushes me harder than anyone else does. It makes me want to be better.” He said it without thinking twice, the truth of it too obvious to feel like a confession.

“Do you worry about him when he’s hurt?”

“Of course I do.” That one came out almost indignant, like the question itself was strange for having to be asked at all. “Why wouldn’t I?”

Ochako nodded slowly, watching him with an expression he couldn’t quite read, something careful and patient underneath it. “Do you pay more attention to him than you do to other people?”

“No,” Izuku said immediately, and then stopped.

He thought about it properly this time, the way he hadn’t with the earlier questions, and the answer started unraveling in his head almost against his will. He thought about how he could read Katsuki’s exhaustion in the set of his shoulders before Katsuki himself would ever admit to being tired. He thought about the specific way Katsuki’s jaw tightened when something was bothering him, a tell so subtle most people never caught it, one Izuku had apparently been cataloguing for years without ever consciously deciding to. He thought about how he could track Katsuki’s mood across a room without needing to hear a single word, how he noticed when Katsuki’s attacks in training carried more force than usual, how he always seemed to know, somehow, when something underneath the surface had shifted.

“Actually,” he said slowly, “maybe. I don’t know. I notice things about him. A lot of things. More than I notice about anyone else, probably, which is weird, right, that’s weird, I don’t think I’ve ever actually said that out loud before.”

Ochako let that sit for a moment before asking her last question, quieter than the ones before it. “Do you think about him when you’re not together?”

“Yes,” Izuku said, and this time there wasn’t even a flicker of hesitation before the word left his mouth.

The silence that followed stretched long enough that he finally looked up from his notebook to see what was taking her so long to respond, and found her watching him with an expression that was somewhere between fond and exasperated, like she was looking at someone who’d just walked directly into an obvious answer without noticing it was there.

“What?” he asked. “Why are you looking at me like that?”

Ochako sighed, long and heavy, and reached over to close his notebook gently before he could write anything else in it.

“Maybe,” she said, “you should think about the answers you just gave me.”

He found Shoto later that evening in one of the common room’s quieter corners, a textbook open in his lap that he didn’t appear to actually be reading, and decided that if anyone in the entire class was going to give him a clear-headed, objective read on the situation, it was going to be Shoto. Ochako had gotten strange and evasive. Tenya kept trying to solve it like an engineering diagram. Shoto, at least, tended to just say things plainly, without wrapping them in anything.

“Can I run something by you?” Izuku asked, dropping down onto the couch across from him.

“Go ahead.”

So he did. He explained the whole thing from the beginning, the sparring match, the notebook entries, the failed experiment that hadn’t failed at all, the pattern he’d spent the entire week trying and failing to unsee. Shoto listened without interrupting once, his expression unreadable the entire time, occasionally turning a page in his textbook like he was still keeping half his attention on it even as he absorbed every word Izuku said.

When Izuku finally finished, Shoto closed the textbook fully and set it aside.

“Do you think you behave differently around him compared to everyone else?”

“No,” Izuku said, a little too quickly. “I don’t think so.”

“Do you get nervous when he gets close to you?”

Izuku paused, thinking back to earlier that day, to the way his chest had tightened every time Katsuki closed distance during their match. “Sometimes.”

“Do you notice when he walks into a room?”

“Yes.” That one didn’t even require thought. It was simply true, had always been true, in a way Izuku had never once questioned before this week.

“Do you want him to pay attention to you?”

Izuku opened his mouth to answer immediately, the way he had with everything else, and then found the words catching somewhere in his throat instead. He thought about every conversation where he’d tried a little harder to say something interesting, every training session where some small, hopeful part of him had wanted Katsuki to actually notice how much he’d improved, every time Katsuki’s attention had landed on him and something in his chest had gone warm and pleased before he could stop it.

“Yeah,” he admitted, quieter than he meant to. “I do.”

Shoto studied him for a moment, calm and steady, then said it exactly the way he said everything else, like a simple observation rather than an accusation. “I think you like him.”

Izuku’s grip on his notebook went slack enough that it nearly slid off his lap entirely. “What? No. No, that’s not, Kacchan’s my childhood friend. My rival. Someone I respect more than almost anyone else at this school. That’s not the same thing.”

“Does any of that explain everything you just told me?”

Izuku opened his mouth to answer, certain the words were right there, certain he had a perfectly reasonable explanation that accounted for the nervousness and the attention and the quiet, persistent want underneath all of it.

Nothing came out, no matter how many times he tried to force something reasonable past the sudden lump in his throat.

He spent the rest of the evening trying very hard not to think about what Shoto had said, which meant, naturally, that he thought about almost nothing else. It followed him through dinner, through the shower he took afterward, through the twenty minutes he spent lying on his bed staring at the ceiling instead of doing the homework spread out beside him. By the time Kirishima came pounding on his door insisting he join everyone downstairs for game night, Izuku was more than ready for any distraction that might actually work.

The common room was already loud by the time he got there, couches and floor space claimed by most of Class 1-A, snacks and drinks scattered across every available surface, some board game half set up on the coffee table while Kaminari and Mina argued over rules nobody had apparently agreed on in the first place. Katsuki was over by the couch, already deep in an argument with Kaminari about whether a rule he was inventing on the spot actually existed, and for a moment Izuku genuinely believed the night might go exactly the way he wanted it to: loud, distracting, blessedly free of anything resembling introspection.

Then someone pointed out the empty spot beside him, and Katsuki dropped down onto it without a second thought, close enough that their shoulders nearly brushed.

Izuku became instantly, painfully aware of the distance between them, or rather the lack of it, and Shoto’s words from earlier surfaced in his head with startling clarity. He tried to focus on the game instead, on the cards in his hand, on literally anything else, but Blackwhip apparently had other priorities that evening.

He felt it before he saw it, a tendril slipping loose from his arm without permission and curling lazily around the leg of Katsuki’s chair. He yanked it back the second he noticed, glancing around quickly to see if anyone had caught it, only to find Ochako watching him from across the room, her expression carefully neutral behind the rim of her drink.

A few minutes later, Katsuki leaned across him to grab the bowl of snacks sitting near Izuku’s knee, and Blackwhip shot out again, wrapping loosely around his wrist before Izuku could stop it.

“Stop,” Izuku muttered under his breath, grabbing at the tendril with his free hand and hauling it back.

Kaminari, unfortunately, had perfect timing. “Is it doing the thing again?” he asked, grinning wide enough that Izuku wanted to disappear directly into the couch cushions.

“It’s not doing anything,” Izuku said, far too quickly.

“That looked like an involuntary activation,” Tenya said, already leaning forward with genuine concern written across his face. “Izuku, are you certain you’re maintaining adequate control?”

“I’m fine. It’s fine. I have it under control.”

From across the room, Shoto glanced up from his own hand of cards, unbothered as always. “Blackwhip seems particularly interested in him tonight.”

“Quirks don’t have interests!” The words came out much louder than he intended, and judging by the heat spreading across his face, everyone within earshot had probably noticed.

Katsuki looked down at the tendril still loosely circling his wrist, then back at Izuku, something unreadable passing briefly across his face. Instead of shaking it off immediately the way he usually did, he left it there a few seconds longer than necessary, long enough that Izuku’s pulse did something complicated, before finally tugging his hand free with the same casual ease he did everything else.

The game continued around them. Izuku tried, genuinely tried, to focus on his cards, on the conversation, on the movie someone eventually put on once the game fell apart into general chaos, but every small thing Katsuki did kept pulling his attention right back. Katsuki laughed at something Kirishima said, sudden and unguarded in a way Izuku rarely got to see. Katsuki reached over and stole a handful of chips straight out of Izuku’s bowl without asking, like he had some standing claim to it. Katsuki’s shoulder bumped against his whenever something made him laugh hard enough to shake, an easy, thoughtless contact that Izuku felt far more acutely than he should have.

He noticed, somewhere in the middle of all of it, how relaxed Katsuki seemed tonight, loose and unguarded around the whole class in a way that softened the sharp edges he usually kept up. And he noticed, with a small twist low in his stomach that he didn’t quite know what to do with, that Katsuki seemed even more relaxed around him specifically, sitting closer without seeming to think about it, comfortable in a way Izuku had never really stopped to examine before.

By the time the movie hit a quiet stretch and most of the room’s attention had settled on the screen, Izuku found himself leaning slightly into Katsuki’s side without remembering when he’d started doing it, the warmth of him solid and familiar beneath his shoulder.

Blackwhip curled around Katsuki’s wrist again, slow and lazy this time, nothing frantic about it at all.

Izuku didn’t pull it back this time, letting it stay curled loosely around Katsuki’s wrist while the movie played on in the background.

He just sat there, staring at the black tendril wrapped gently around Katsuki’s wrist, listening to the steady thrum of his own pulse as the possibility he’d been avoiding all week finally began to take shape.

Across the room, Ochako noticed, but this time she didn’t say anything. Izuku barely noticed her watching him, too caught up in the strange, uncomfortable feeling settling somewhere deep in his chest, the one that made him wonder if he’d been looking for the wrong answer all along.

Somewhere, Izuku started noticing something else, something he genuinely couldn’t decide was new or if he’d simply never paid close enough attention before this week to catch it. Katsuki seemed to be around him constantly. He dropped into the seat beside Izuku during study sessions without asking, claimed the spot next to him during group assignments even when there were other open seats scattered around the room, leaned over his shoulder to check his notes with a casualness that suggested this was completely normal, nothing worth remarking on at all.

Izuku genuinely couldn’t tell if it was intentional. Katsuki had never been the type to explain his own behavior, let alone examine it out loud, and asking directly felt like inviting a level of scrutiny Izuku wasn’t remotely ready to survive. So instead he just kept quietly cataloguing it, the way he catalogued everything, and tried not to notice how much closer Katsuki seemed to be standing lately compared to before.

Blackwhip noticed regardless of whether Izuku wanted it to.

It happened again during a study session in the library, the two of them tucked into a corner table with notes spread out between them, working through a chemistry problem set that Izuku had been half-heartedly attempting to focus on. Katsuki leaned over without warning, close enough that Izuku could feel the warmth coming off him, scanning the page of notes Izuku had been scribbling.

“You wrote that wrong,” Katsuki said, tapping a finger against one of the equations.

Izuku barely registered the correction, too distracted by how close Katsuki’s face suddenly was to his own, and that was exactly when the tendril slipped loose and curled around Katsuki’s wrist before he could stop it.

Katsuki didn’t pull away this time either. He just looked down at it, unhurried, studying the black tendril wrapped snugly around his skin as though he were actually trying to understand what it wanted.

“Why does it keep doing that?” he asked, his tone almost thoughtful instead of irritated.

“I genuinely don’t know,” Izuku said, and meant it completely. “I’ve tried everything. It just, does this. Around you specifically.”

Katsuki was quiet for a moment, still watching the tendril, an expression on his face that Izuku couldn’t quite decode. “Maybe your quirk’s trying to tell you something.”

Izuku laughed, quick and awkward, mostly out of reflex, assuming the comment was some kind of jab wrapped up in false sincerity, the way Katsuki’s teasing usually worked. “Yeah, right.”

Katsuki didn’t laugh along with him. He just shrugged, easy and unbothered, and finally tugged his wrist free before going back to pointing out the mistake in Izuku’s chemistry notes like nothing had happened at all.

Izuku tried to let it go, tried to focus on the corrected equation now sitting in front of him, but the comment lodged somewhere behind his ribs and refused to leave for the rest of the night, long after Katsuki had packed up his things and headed back to his own room.

Tenya, predictably, decided the situation called for something more rigorous than anecdotal observation, and by the following afternoon he’d organized an actual controlled experiment, complete with a hand-drawn diagram and measured distances marked across the training room floor. Part of it, Izuku suspected, came from genuine concern about his quirk control. The rest of it, Izuku was fairly certain, came from Tenya simply wanting a definitive answer to a problem that had been bothering all of them in one form or another for over a week.

“The methodology is straightforward,” Tenya said, gesturing toward the chalk marks with the kind of enthusiasm he usually reserved for subjects considerably more dignified than this. “Several classmates will stand at incremental distances from you. You’ll activate Blackwhip under controlled conditions, and we’ll observe whether proximity correlates with the reaction we’ve documented.”

“This feels like a bad idea,” Izuku said.

“It’s excellent data collection.”

Ochako, Kirishima, and Mina took up positions at the first three marks, spaced out at varying distances, and Izuku reached for the quirk with a resigned sort of dread settling low in his stomach. The tendrils responded exactly the way they were supposed to, reaching for each of them in turn with clean, obedient precision, nothing unusual about any of it.

“Baseline confirmed,” Tenya said, scribbling something onto his clipboard.

Then he waved Katsuki forward, and the real test began.

Katsuki started at the farthest mark, arms crossed, looking supremely unbothered by the entire exercise. Nothing happened. He took a step closer. Still nothing. Izuku allowed himself a small flicker of hope that maybe this time would actually be different, maybe the whole thing really had been some kind of fluke after all.

Katsuki took another step, just as casually as before, apparently unconcerned with whatever experiment Tenya thought he was running.

One of the tendrils twitched against Izuku’s arm, subtle but unmistakable, and Tenya’s pen moved immediately across his clipboard.

“Noted reaction at four meters,” he said, sounding entirely too pleased about it.

Katsuki kept advancing, closing the distance one measured step at a time, and with every step Izuku could feel Blackwhip responding more strongly, the faint twitch against his arm turning into a pull he was no longer sure he could call accidental. By the time he’d crossed the last mark and stopped directly in front of Izuku, close enough that Izuku had to tilt his head slightly to keep eye contact, one of the tendrils had already lifted from his arm and wrapped itself snugly around Katsuki’s wrist without any input from Izuku at all.

“Fascinating,” Tenya breathed, leaning in to study the reaction like he’d just witnessed something groundbreaking. “The correlation is remarkably consistent. Nearly linear, in fact.”

“I hate this,” Izuku muttered, face burning as he retracted the tendril with as much dignity as he could manage, which wasn’t much.

Shoto, standing off to the side with his arms crossed, offered his verdict in the same flat, unbothered tone he always used. “The results seem fairly conclusive.”

“Conclusive of what?” Izuku asked, though some small, cowardly part of him already suspected he didn’t actually want the answer.

Nobody responded immediately. Tenya was too absorbed in his notes to look up. Shoto simply raised an eyebrow, apparently convinced he’d already said enough. Ochako, standing a little apart from the rest of them, wore an expression that made it painfully obvious she knew exactly what the data meant, though she wasn’t offering to say it out loud any more than she had the first time he’d asked.

“What does it mean?” Izuku tried again, looking between all three of them.

Tenya cleared his throat and mumbled something vague about needing additional trials to establish full statistical confidence. Shoto simply shrugged. Ochako gave him a small, knowing smile, the kind that made it painfully obvious she had an answer and had no intention of giving it to him, before turning to help Mina put the chalk marks away.

Izuku stood there in the middle of the training room, Katsuki still close enough that he could feel the lingering warmth of him, and realized that apparently nobody intended to give him a straight answer.

They were doing another team exercise this time with class 1-B, a straightforward capture drill that had gone smoothly until the moment everything changed. Izuku wasn’t even paired with Katsuki this time. He was on the opposite side of the training ground, focused on his own assignment, but he still caught the exact moment Katsuki took a hit he hadn’t fully braced for, a heavy blow from Tetsutetsu’s hardened fist that sent him skidding across the ground.

Something in Izuku’s chest lurched, sudden and violent, a spike of panic so sharp it felt physical.

He didn’t decide to activate Blackwhip. There was no conscious thought behind it, no deliberate reach for the quirk the way there always was, just pure animal reaction, and the tendrils exploded from his arm before he’d even processed what he’d seen. They shot across the training ground in a single fluid burst, closing the distance in seconds, and wrapped tightly around Katsuki’s torso, hauling him backward and out of Tetsutetsu’s immediate range before anyone else had time to react at all.

The training ground went quiet, everyone’s attention snapping toward the two of them at once.

Izuku stood frozen, staring at his own hands like they belonged to someone else, his heart still hammering so hard he could feel it in his throat. He’d never activated Blackwhip like that before, not with that kind of speed, not without the smallest sliver of intent behind it. It had simply happened, faster than thought, the instant his mind registered Katsuki in danger.

Katsuki, still wrapped loosely in black tendrils, pushed himself up onto one elbow, looking more annoyed than hurt. “Oi. You good?”

Izuku blinked at him, uncomprehending for a second. “What?”

“You look like you’re about to pass out.” Katsuki peeled the tendril off his arm without much urgency, sitting up fully now, red eyes narrowed with something that looked almost like concern buried under the usual irritation. “I’m fine. Barely even hit me.”

Izuku became distantly aware that his hands were shaking. He pressed them against his thighs, willing them to be still as he tried to slow his frantic heartbeat, and realized with a jolt of embarrassment that Katsuki was right. He was the one who looked shaken, not the other way around, standing there pale and trembling over an injury that hadn’t even been serious enough to warrant a trip to Recovery Girl.

Ochako had noticed too. She was watching from a few feet away, her expression unreadable, though her eyes kept moving between Izuku and Katsuki with a quiet understanding Izuku didn’t want to examine.

She found him again later, after the exercise had ended and the class had scattered back toward the locker rooms, catching his arm gently before he could disappear into the crowd.

“Can I say something?” she asked, voice low enough that only he could hear it.

“I don’t think Blackwhip’s reacting to him,” she said, choosing her words carefully, watching his face the whole time she spoke. “I think it’s reacting to how you feel about him.”

Izuku opened his mouth, an automatic protest already forming, but the words never made it past his throat. He thought about the spike of panic, sharp and immediate and entirely disproportionate to what had actually happened. He thought about the tendrils moving before he’d consciously told them to, faster and surer than anything he’d ever managed to summon on purpose.

He didn’t have an answer for her, not one he was ready to say out loud, so he let the question hang between them instead.

Ochako gave his arm a small, gentle squeeze, then let go and walked toward the locker room without pushing him any further, leaving Izuku standing there as her words settled somewhere deep inside him, heavier now that he couldn’t quite dismiss them.

Somewhere in the days that followed, Izuku started paying less attention to Blackwhip and more attention to himself, which had to be a considerably more uncomfortable exercise than any of his quirk research had been so far.

He noticed it first in small ways, the kind of thing that would have slipped past him entirely a week ago. He caught himself scanning a room the second he walked into it, some automatic part of his brain checking for Katsuki’s presence before he’d even consciously decided to look. He noticed the empty desk during homeroom on the one morning Katsuki showed up late, felt a strange flicker of unease before he’d even registered why the room seemed slightly off. He could read Katsuki’s irritation from across a classroom before anyone else seemed to catch it at all, some subtle shift in his shoulders or the set of his jaw that Izuku had apparently been tracking for far longer than he’d ever admitted to himself.

The more he started looking for evidence, the more he found, until ignoring it became almost as exhausting as acknowledging it.

He knew, without ever having consciously memorizing it, that Katsuki took his coffee black, no sugar, and drank it too hot every single time out of pure stubbornness. He knew which shoulder still bothered him after a long training session, the left one, the one he favored subtly whenever he thought no one was watching. He knew which assignments frustrated Katsuki most, anything requiring long stretches of paperwork instead of action, and could predict the exact moment Katsuki’s patience for a task would finally snap. He even knew the specific, barely-there way Katsuki’s mouth twitched when he was secretly pleased with himself but too proud to actually show it, a tiny almost-smile he tried and usually failed to smother before anyone caught it.

He’d never sat down and decided to memorize any of it; somehow, his mind had simply been keeping track all these years without asking permission.

He sat with that realization during class, notebook open in front of him, half listening to Present Mic explain something about hero law while a much more uncomfortable question kept circling through his head. Months. Years, maybe. Long enough that it had become so ordinary he’d never once stopped to question why he knew these things at all, why his brain had apparently decided Katsuki was worth this much quiet, careful attention when nobody else in his life got anywhere close to the same treatment.

He glanced over without really meaning to, drawn by pure habit toward the desk in front of him, and found Katsuki mid-yawn, one hand dragging through his hair, entirely unaware he was being watched.

Izuku looked down fast, face heating, heart doing something distinctly unhelpful in his chest, and stared very hard at his own notes for the rest of the period instead.

They ended up sitting together after training that afternoon, both of them wiped out from an unusually brutal session, sprawled against the wall of the gym with water bottles they were too tired to actually drink from. Izuku’s whole body ached in that specific, satisfied way that only came after real exertion. For a while neither of them said much, just sat there in comfortable silence while their heart rates settled back to normal.

Then Katsuki noticed the scrape, his attention snagging on it before Izuku had even thought to hide his hand.

“You’re bleeding,” he said, nodding at Izuku’s hand without much alarm.

“It’s fine, it’s just a scrape.”

Katsuki reached over anyway, catching Izuku’s wrist and turning his palm upward to actually look at it, entirely casual about the whole thing, the kind of thoughtless contact he offered without a second thought a dozen times a week. His thumb brushed lightly over the edge of the scrape, checking how deep it went.

Izuku’s entire body reacted like it had been struck by lightning.

His heart slammed against his ribs, hard and sudden, heat rushing up his neck and into his face so fast it was almost dizzying, and before he could do anything to stop it, Blackwhip surged out from his other arm and curled snugly around Katsuki’s wrist.

Both of them went still, the moment stretching out awkwardly between them while neither seemed to know what to do next.

Izuku stared down at the tendril, at his own hand still held loosely in Katsuki’s, at the black coil wrapped around Katsuki’s wrist like it had every intention of never letting go, and felt something in his chest crack open with sudden, undeniable clarity.

Katsuki looked at their hands too, then up at Izuku, something searching in his expression that Izuku couldn’t quite meet.

The problem had never been Katsuki simply being there. Blackwhip wasn’t reacting to Katsuki himself so much as everything Katsuki stirred up inside him, every spike of nervousness, every flare of concern, every quiet feeling Izuku had spent years giving other names simply so he wouldn’t have to examine them too closely.

His mind went back through every time Blackwhip had reached for Katsuki without permission. The sparring match, the training room doorway, the wrist grabbed to pull him from an explosion, the protective burst that had hauled him out of Tetsutetsu’s reach faster than conscious thought could ever move. It had never been random, not at all. He’d only thought it was strange while he was still looking for an explanation that didn’t require him to confront what had been sitting underneath it all along.

For the first time since Shoto had said it out loud, the idea didn’t feel ridiculous at all.

It felt, terrifyingly, like it might just be true.

Izuku panicked, his mind scrambling for any exit that didn’t involve explaining what had just happened.

“I’m not feeling well,” he blurted, already scrambling to his feet, tugging his hand free of Katsuki’s grip a little too fast. “I think I should, I should go lie down.”

“You look kind of pale,” Katsuki said, frowning, and the concern in his voice only made it worse.

“I’m fine, I’m just tired. Training. It’s a lot. I’ll see you tomorrow.”

He didn’t wait for a response, just grabbed his bag and fled the gym at a pace that was probably too fast to actually pass as casual, and spent the entire walk back to his dorm trying not to think about the look on Katsuki’s face right before he’d bolted.

From that point on, avoidance seemed like the only reasonable strategy. Maybe if he gave himself enough room to breathe and think without Katsuki constantly scrambling his thoughts, Blackwhip would settle down and the whole situation would finally become manageable. He started arriving to class a few minutes late so he wouldn’t have to make small talk before homeroom. He found reasons to sit elsewhere during meals. He turned down an invitation to train together on Tuesday, citing a made-up study session that didn’t actually exist.

It worked for approximately as long as it took him to realize that avoiding Katsuki hadn’t made anything easier.

If anything, the quirk seemed to grow more restless the less he saw Katsuki, as though the absence itself had become another kind of trigger. He caught himself suppressing small twitches of the quirk at odd moments throughout the day, phantom pulls toward nothing in particular, an unsettled energy sitting just under his skin that refused to calm down no matter how far he stayed away.

By Wednesday afternoon, he’d given up on pretending he could think his way out of it, sitting alone in his room with the curtains drawn while the same impossible conclusion kept circling back no matter how many times he tried to push it away. He liked Katsuki. He might really like Katsuki, in the way that made his chest ache and his pulse race and every one of Blackwhip’s inconvenient reactions suddenly make perfect, horrifying sense.

He was still sitting there, knees pulled up to his chest, notebook abandoned on the floor beside him, when Ochako found him.

She let herself in without much ceremony, the way she always did, and took one look at him curled up in the dim room before settling down on the floor across from him. “Why are you hiding?”

Izuku opened his mouth to deny it, then closed it again, too exhausted to bother lying to her on top of everything else.

“I think you were right,” he admitted, quiet and a little strangled. “I think I might like him. Kacchan. I might, actually, genuinely like him.”

Ochako’s whole face lit up, bright and delighted, and Izuku immediately knew she’d been waiting for him to figure this out on his own.

“Finally,” she said, grinning.

“You knew?”

“I suspected pretty strongly, yeah.” She scooted closer, bumping her shoulder against his. “You two have been doing this weird thing for years where you’re constantly paying attention to each other and pretending it means nothing. It was kind of obvious once Blackwhip started making it literal.”

Izuku groaned, dropping his forehead against his knees. “This is a disaster.”

“It’s not a disaster.” Ochako’s voice softened, patient in a way that helped loosen something tight in his chest. “You don’t have to do anything about it right now. Realizing you like someone doesn’t mean you have to march up and confess on the spot. You’re allowed to just, sit with it for a while. Figure out what you actually want before you figure out what to do.”

Izuku lifted his head, studying her carefully. “That’s actually helpful.”

“I have my moments.”

They sat together for a while longer after that, Ochako filling the silence with easy, undemanding conversation about nothing in particular, and by the time she finally left him alone, Izuku felt something complicated settle in his chest, terror and relief tangled together in equal measure, the fear was still there, but it no longer felt quite as impossible now that he’d finally stopped pretending he didn’t know what it meant.

It took less than two days for Katsuki to notice, which honestly should have been the least surprising part of the whole thing, given exactly how observant he could be when he actually cared to pay attention. Izuku had barely finished changing after evening practice when his bedroom door swung open without so much as a knock, and Katsuki stepped inside and shut it firmly behind him.

“Okay,” Katsuki said, arms crossed, planting himself directly between Izuku and any hope of escape. “What the hell has been going on with you.”

Izuku’s stomach dropped straight through the floor. “Nothing’s going on.”

“Bullshit.” Katsuki’s eyes narrowed, sharp and unrelenting in a way that made it clear he had no intention of leaving without an actual answer. “You’ve been avoiding me for a week. Skipping lunch. Bailing on training. Practically sprinting out of rooms whenever I show up. I’m not an idiot, Deku.”

“It’s complicated,” Izuku tried, already backing toward his desk like putting furniture between them might somehow help.

“Uncomplicate it.” Katsuki didn’t move, just kept watching him with that same unwavering focus. “Does this have something to do with Blackwhip?”

Izuku went quiet, the silence stretching long enough to answer the question on its own.

“It does, doesn’t it.” Katsuki’s voice dropped slightly, less accusatory now and more genuinely curious. “What did you figure out?”

Izuku stared at the floor, at his own hands, at literally anything that wasn’t Katsuki’s face, scrambling for some way to explain something he still barely understood himself. “I think,” he started, then stopped, then started again. “I think Blackwhip’s been reacting to my feelings. Not to you specifically. To how I feel when you’re around.”

His face was already burning by the time he finished the sentence.

“What feelings?” Katsuki asked, quieter than before.

“I don’t know how to explain it.” The words came out in an unsteady rush once he finally started, like something dammed up too long finally breaking loose. “I get nervous when you’re close. I always want you nearby, even when I don’t have a reason to. I worry about you constantly, way more than I should, and I think about you more than I probably should too, all the time, even when we’re not together. And when you touch me, it’s, it’s different than when anyone else does. I don’t understand why. It just is.”

Katsuki didn’t say anything. He didn’t laugh either, didn’t make some sharp comment to deflect, just stood there listening with an intensity that left Izuku nowhere left to hide.

The silence stretched out, heavy and unbearable, until Izuku finally forced the last piece of it out in a voice barely above a whisper.

“I think I like you.”

The moment the words left his mouth, Blackwhip surged forward on its own, curling gently around Katsuki’s arm and tightening there, soft but certain, like it had been waiting the entire time for Izuku to finally say out loud what it had already known.

Izuku’s entire brain short-circuited for a moment, still catching up with what he’d just said out loud, when Katsuki spoke again.

“Yeah, I figured.”

Izuku’s head snapped up so fast he nearly gave himself whiplash. “What?”

“I said I figured.” Katsuki looked entirely too pleased with himself, arms still crossed, watching Izuku’s mortification unfold with obvious amusement. “Blackwhip wasn’t exactly subtle about it. And you’re not much better, honestly. You get this whole look on your face whenever I’m around. Kind of hard to miss after a while.”

“You knew?” Izuku’s voice cracked slightly on the word. “This whole time, you knew, and you didn’t say anything? How long have you known?”

Katsuki shrugged, infuriatingly unbothered. “A while.”

“That’s not an answer!”

“It’s the answer you’re getting.” Katsuki’s mouth twitched, clearly enjoying this far more than the situation warranted. “Took you long enough to figure out what basically everyone else already noticed, by the way. Ochako’s known for weeks.”

Izuku groaned and buried his face in his hands, heat crawling up the back of his neck. “This is humiliating.”

“It’s a little funny,” Katsuki said, and Izuku could hear the grin in his voice without even looking up.

He forced himself to lift his head anyway. There was still one question sitting heavier than all the embarrassment combined, the only one that actually mattered right now. “Do you,” he started, then had to force the rest of it out before he lost his nerve entirely. “Do you like me too?”

Katsuki didn’t answer right away, taking his time with it in a way that made Izuku’s stomach twist tighter.

The pause stretched long enough for every worst-case scenario to flood Izuku’s mind at once, until Katsuki finally exhaled and looked directly at him.

“Yeah,” he said, simple and unguarded in a way Izuku rarely got to see. “I do.”

“Really?”

“Would I have kept letting your quirk wrap around my arm every five minutes if I hated it?” Katsuki’s expression softened slightly, the teasing edge easing back just enough to let something more sincere through. “I’m not exactly known for putting up with shit I don’t want.”

Izuku stared at him, and suddenly every strange, amused look Katsuki had been giving him over the past week clicked into place at once, all of it recontextualized in a single, dizzying moment. The way he hadn’t pulled his wrist back immediately. The way he’d left it there, watching, waiting, letting Blackwhip do the talking neither of them had been brave enough to do out loud.

“You’ve been enjoying this,” Izuku said slowly. “This whole time.”

“A little bit, yeah.” Katsuki’s grin came back, softer this time. “Watching you panic about your own quirk grabbing me was kind of the best part of my week, not gonna lie.”

For a long moment after that, neither of them moved, the two of them just standing there in the middle of Izuku’s bedroom with everything finally out in the open and no clear idea what to actually do about it. Izuku’s heart was still hammering, nerves buzzing under his skin in a way that had nothing to do with fear anymore and everything to do with the sheer weight of what had just happened between them.

Katsuki, for his part, looked considerably less uncertain, watching him with an expression that was equal parts patient and expectant, like he was perfectly content to let Izuku set the pace here even though it was obvious he already knew exactly what he wanted.

Izuku took a breath, gathered whatever scraps of courage he had left, and closed the distance between them.

The kiss was tentative at first, clumsy in the way first kisses tended to be, Izuku barely brushing his lips against Katsuki’s like he half expected to be pushed away. He wasn’t. Katsuki responded almost immediately, one hand coming up to rest against the side of Izuku’s jaw, steady and sure in a way that settled every nervous flutter in Izuku’s chest into something warm and slow instead.

That was, of course, exactly when Blackwhip decided to make its opinion known.

Tendrils erupted from Izuku’s arms all at once, wrapping enthusiastically around Katsuki’s waist, his wrist, one even looping loosely over his shoulder, like the quirk had been waiting its entire existence for permission to finally hold on properly.

Izuku broke the kiss immediately, staring down in absolute horror at the sheer volume of black tendrils currently wrapped around his boyfriend, if that was even the right word yet, since he hadn’t gotten that far.

Katsuki started laughing, loud and genuine, head tipping back with it.

“This is humiliating,” Izuku said, face burning as he tried, mostly unsuccessfully, to coax the tendrils back into submission. “It’s really happy about this and I hate it.”

“It’s not wrong, though.” Katsuki was still grinning, clearly delighted by the entire disaster, making no effort whatsoever to extract himself from the tangle currently holding him in place. “Pretty solid endorsement, honestly.”

Izuku groaned, but the mortification had already softened into something closer to helpless fondness, and after a moment he let himself smile too, sheepish and a little dazed, before finally managing to coax Blackwhip back under control.

“Come here,” he said instead, tugging Katsuki by the wrist toward the bed, feeling bolder now than he had all evening.

Katsuki went easily, kicking off his shoes and dropping down onto the mattress with none of his usual bluster, and Izuku curled up beside him like they’d done this a hundred times before instead of never at all. They talked for a while after that, quiet and unhurried, about nothing in particular, Katsuki’s arm slung loosely around him and Izuku’s head tucked against his shoulder, the whole thing settling into something surprisingly, easily comfortable.

Katsuki fell asleep first, mid-sentence, his voice trailing off into soft, even breathing before he’d even finished whatever complaint he’d been making about training schedules.

Izuku glanced at the clock and huffed out a quiet laugh. It was well past what he was fairly sure counted as Katsuki’s actual bedtime, the exact kind of thing Katsuki would deny to his last breath if anyone ever brought it up. He reached over and switched off his All Might lamp, plunging the room into soft darkness, and settled back against Katsuki’s side.

For the first time in longer than he could remember, he fell asleep warm.

Izuku walked into class the next morning with the singular, desperate hope that nobody would notice anything different, which turned out to be an entirely unrealistic goal roughly four seconds after he stepped through the door.

Blackwhip, apparently having no intention of behaving itself now that Izuku had finally stopped fighting it, was still curled loosely around Katsuki’s wrist, the two of them walking into class side by side like this was a completely ordinary thing to be doing.

Ochako spotted it first, her eyes going wide before a slow, delighted grin spread across her face.

Shoto noticed next, glancing between the tendril and Izuku’s expression with the same quiet, unbothered curiosity he brought to everything.

Then Tenya’s gaze landed on it too, and his eyebrows shot up. “Izuku. Have you finally identified the cause of the unusual Blackwhip activity?”

Izuku’s entire face went up in flames. “I, um, sort of, yes.”

That was all the confirmation Mina needed. She sat bolt upright in her seat, spinning around with the kind of energy that suggested she’d just uncovered the single best piece of gossip of her entire school year. “Wait. Wait, did something happen?”

“Something happened,” Kaminari said, already grinning, leaning across his desk toward them. “What happened? Tell me everything.”

Kirishima looked between Izuku and Katsuki, taking in the tendril still wrapped around Katsuki’s wrist, and an enormous grin slowly spread across his face. “Oh my god.”

“I figured out the problem,” Izuku tried, desperately attempting to steer the conversation somewhere he could actually survive. “That’s, that’s really all there is to it.”

“That is very obviously not all there is to it,” Mina said.

Shoto, unhelpfully, chose that exact moment to offer his own commentary. “The explanation seems fairly obvious at this point.”

“Please, everyone, let’s not interrogate him,” Tenya said, holding up both hands in an attempt to restore some order, though his own curious glances toward Katsuki’s wrist rather undercut the effort.

Ochako caught Izuku’s eye from across the room, wearing an expression of pure, smug satisfaction that made it painfully clear she considered herself at least partially responsible for this and fully intended to take credit for it later.

Katsuki, predictably, had reached the absolute limit of his patience. “Oi!” he snapped, glaring at the entire classroom with enough heat to make several people flinch back in their seats. “Mind your own damn business, all of you!”

Nobody actually stopped looking. If anything, the yelling made everyone even more convinced that something had happened, and the whispers grew louder as Izuku sank down into his seat and wished, quietly and hopelessly, that the floor might open up and swallow him whole.

By the time everyone actually settled down, the whispering had mostly faded into background noise, though Izuku suspected Mina would keep bringing it up for considerably longer than anyone else wanted her to. He gathered his things at the end of the day still faintly embarrassed by how quickly the whole class had figured it out, how effortlessly his own quirk had given him away before he’d even had the chance to explain anything on his own terms.

Katsuki fell into step beside him as they left the classroom, unbothered as ever, and reached over to take his hand without any particular ceremony, like it was simply the obvious thing to do.

Blackwhip responded immediately, curling loosely around their joined wrists in one smooth, contented motion.

Izuku looked down at it, watching the black tendril settle comfortably against Katsuki’s skin, and felt something in his chest finally, fully unclench. For weeks he’d treated this exact behavior like a malfunction, something broken that needed correcting, hours spent hunched over notebooks trying to diagnose a problem that had never actually been a problem at all. It had simply been telling him something long before he was ready to hear it, patient and stubborn in a way he hadn’t been able to ignore no matter how hard he tried.

“You gonna retract that?” Katsuki asked, glancing down at the tendril without much urgency.

Izuku considered it for a moment, weighing the impulse to pull it back against how little he actually wanted to, and decided to leave it exactly where it was.

He let Blackwhip stay exactly where it was, wrapped snug around both their wrists as they walked together down the hallway, and for the first time in weeks felt no need to fight it or wonder what it meant.

His quirk had understood his own feelings before he did. He was, finally, more than a little relieved to have caught up.