The first Izuku remembers of his peculiar Quirk is when he was seven, three years after the doctor had declared him officially Quirkless. Even despite the diagnosis, he still held out hope, and continued to analyse the Quirks of Pro Heroes as well as his classmates'.
He may have been desperately hoping, but that didn't mean he was excited when he finally discovered it – no, in fact, quite the opposite – he was terrified. It was early evening, and Izuku had gone to have a shower before going to bed, but the moment he took off his clothes all he could do was shriek in horror.
That was how he realised that he could change forms between male and female.
He spent the weekend trying to get used to it, slightly unsettled with the way he could feel his insides practically squirming with every shift, but determined nonetheless. Inko was relieved to see him look so joyful again after the words that had crushed him years previously, and she helped him research all he could about similar Quirks to his.
Monday couldn't arrive quick enough for him, since he couldn't wait to tell Kacchan.
But then... He realised that the boys and the girls never played together, and he wanted to stay friends with Kacchan. The smile faded from his face, and he never spoke a word of his newfound Quirk to anyone besides his mum.
There were times when he accidentally transitioned during the day, but since he was young that meant no-one ever noticed, much to his relief. Over the years, he gained better control over it, learning the way it worked and uncovering strengths and weaknesses.
If there was a time limit to his female form, he had yet to reach it, and he'd spent over a month as a girl before. Besides the queasy feelings of his insides shifting and parts of his body morphing as he grew older, there didn't seem to be a downside besides a dull ache that was no worse than growing pains. He also noticed that any injuries on one form wouldn't carry over to the other one, which implied that he was practically becoming two entirely different people - the idea fascinated him, although he wasn't quite sure what applications that ability would have when he became a hero.
His mother enthusiastically helped him fit in when he was a girl, happily buying dresses, skirts, and form-fitting outfits, as well as make-up and feminine hygiene products. Most of the time, Izuku preferred to stick with the same clothes he wore as a guy, but it was sometimes fun to dress up and go out to experience the world a whole other way.
When the taunts and bullying at school got too much, he was often sorely tempted to shift before their eyes to revel in their shock, but held his tongue when he remembered the perverted words his teenaged classmates would often mutter whenever a girl was around - he didn't want to be the focus of that.
Fate twisted him a tricky tale, and he found himself at the school he'd always dreamed of attending with All Might's powerful Quirk to assure his place in the Hero Class.
Izuku stared heatedly down at Mineta as the boy made another inappropriate comment towards a female classmate. He really didn't want to intervene in case he caused a scene, so he hoped that the tiny pervert would have some sort of survival instinct and just shut his-
Mineta not-so-subtly flicked his pen off his desk as a girl walked by. “Hey, Yaoyorozu, could you pick up my pen?”
No, don't fall for it-
Of course, Momo was all too naïve and always willing to help a classmate, even if said classmate had verbally and physically harassed her before. She bent over without hesitation, and Mineta immediately started drooling. A few appalled noises came from various other students at his reaction. Just when Izuku thought it couldn't get any worse, the pervert started to reach a trembling hand towards the girl.
Okay, that's it.
Izuku leaned back in his chair, drew back an arm and lightly slammed his fist into Mineta's face, causing the boy to topple backwards off his chair and land with a thud on the floor. He briefly glanced at his knuckles before wrinkling his nose in disgust and wiping the blood off on his trousers. When he looked up again, he immediately froze, his cheeks flushing with embarrassment as he saw everyone staring at him.
Momo seemed ready to scold him once she righted herself, but she frowned and put two and two together. She paused, staring down at the catatonic pervert, before smiling at her guardian angel.
“Thank you, Midoriya-kun. I should have been more careful.” She nodded at him kindly before abruptly placing the pen on Mineta's desk and continuing on her way to the front of the class.
Kirishima continued to stare with awe dancing across his features. “Dude, that was so manly!”
“A-ah, well, s-someone had to do it,” he muttered sheepishly, running a hand through his wild hair to try and dispel some of his nerves.
Kacchan merely snorted and turned back around in his seat.
Izuku knew the signs.
Ashido had been shifting uncomfortably in her seat all day, her hands often clenching over her stomach and her face contorting with subtle pain. She almost burst into tears when they had to do some physical exercise, and she excused herself to the toilets in almost every lesson.
He had only suffered through a few periods in his life, but that was a few too many – he didn't know how girls managed to deal with it every month – and he always made sure to have some useful supplies with him so he could try and make their lives a little easier.
The moment the day ended, Ashido had sprinted off towards the dorms with a herd of sympathetic girls following after her. After a few minutes of chatting, Izuku managed to slip away from the boys and dart off towards his room. He rummaged through his drawers and picked out a box of chocolates and a heat pad before going down to the common room.
Ashido was curled up on the sofa, crushing a pillow to her chest and whining. Uraraka sat next to her, lightly patting the pink girl's hair. Hagakure sat on her other side, possibly rubbing circles into her back. Yaoyorozu and Tsu seemed to be conversing about what movie to watch, while Jirou was sifting through the contents of the fridge and visibly growing more frustrated by the second.
Uraraka looked up, noticing the boy's approach. “Oh, Deku-kun! I thought the boys were going to do some sparring?”
“Leave me to die in peace, Midoriya!” Ashido wailed, pressing her face into the cushion.
He cast her a sympathetic glance, not that she could see. “They are, but I noticed Ashido-san wasn't too well, so I- uh... I brought some gifts that might help...?”
Izuku walked around in front of the sofa, awkwardly offering the two items in his grasp. Ashido peeked over the top of the pillow, glancing between his face and the presents with what looked like disbelief before she chucked the pillow aside and threw herself at the boy, wrapping her arms tightly around him. He stumbled back a step, handing the heat pad and chocolates to Uraraka so he could hug Ashido back, laughing uncertainly as she started to cry.
“You're amazing, Midoriya!” She wept, beaming up at him like he hung the moon. “You've saved me from a world of horrible agony – I love you so much!”
He hesitantly patted her back, an expression of vague amusement playing on his features at her exuberant display of affection. “U-uh, it's, um... no problem?”
She pulled away, only to tug at his hand until he was shoved onto the sofa, almost crushing Uraraka who squeaked in alarm and shuffled to the side before she was sat on. Ashido slumped down next to him, grabbing the heat pack and shoving it on her stomach before leaning against his shoulder with a content sigh.
“I thought it was girls' night?” Jirou asked with an eyebrow raised at the scene.
“Midoriya is an honourary girl. His offerings pleased me. He shall stay,” Ashido insisted, not relinquishing her grip on his arm.
“We're just going to be watching movies and eating snacks, it's not very exciting,” Yaoyorozu informed him, “I'm sure you'd prefer to-”
“No, no!” His cheeks immediately darkened, highlighting the freckles. “No, I'm- uh, I'm fine to stay, it's okay. I used to have movie nights with my mum when I was younger, so this will be fun!”
It didn't take long for them all to be settled down, occasionally nabbing a chocolate from the box as they watched the film in a comfortable silence, broken only by Ashido yelling at the stupidity of the characters onscreen that made everyone laugh at her exasperation.
Eventually, it became a habit for Izuku to bring the girls' presents when they were down, and he became a permanent addition to girls' night. After Ashido had claimed that he made a great teddy bear – and smelt nice, apparently – and Tsu had confirmed it, he found himself happily sitting next to whichever girl was going through hell and letting her snuggle up against him.
After a particularly gruelling day of training, all the girls had fallen asleep during the movie, with Jirou leaning heavily against his side and Hagakure napping on his shoulder. Since he was used to brutal exercise regimes after training with All Might, Izuku was left awake, not daring to move a muscle in case he woke anyone. The sound of the elevator doors opening caught his attention, and he glanced over his shoulder to see who had arrived, only to freeze up nervously as he saw the rest of the boys had returned from whatever it was they'd been doing.
“Oh, so this is where you go when you run off,” Kaminari exclaimed, striding up to him with purpose, only to pause as he took stock of the situation. “...what- Midoriya, that's so unfair! How did you get so many girls-”
“Shh!” Izuku hissed, tensing up when Jirou shifted in her sleep. “Don't wake them.”
“Teach me your ways,” Mineta breathed, already staring intensely with a predatory gleam in his beady little eyes.
Iida pressed the pervert's face between his two hands, lifting him into the air like an idiot sandwich. Izuku shot him a thankful look, which the class rep answered with a noble nod. Sero and Kirishima cautiously approached Ashido, who had made a nest of cushions on the floor and was snoring loudly.
The red-haired boy lightly poked her shoulder until she stirred. “Hey, we were supposed to study today!”
She squinted at him blankly. “Mhm. It's girls' night. No studying.”
Sero snickered, “How can it be girls' night with Midoriya here?”
She shifted her gaze, offering a clumsy wave to Izuku, who returned it, before looking back to her friends. “He is a saviour and a gentleman.”
“And a good pillow,” Hagakure added sleepily, raising her invisible head to peer around at the newcomers.
“What the fuck.” Kacchan muttered, glowering at his childhood friend.
Izuku could only chuckle sheepishly with red tinting his cheeks.
“Ah, Midoriya-kun, wait!”
He stopped in his footsteps, glancing back to see Yaoyorozu jogging up to him. She took a moment to regain her breath, one hand resting on his shoulder.
“U-uh, would you mind checking on Ochako-chan for me? She didn't come out of her room this morning, and when I called to her she sounded distressed. I'd have helped her out myself, but I have a meeting I'm already late for. Since you're her best friend, I just thought...” She trailed off as he nodded his assent, already lightly patting her back to reassure her.
He smiled at her. “Go to your meeting, I'll go check on her!”
The girl visibly relaxed, already rushing off down the corridor. “Thank you, Midoriya-kun!”
Izuku's smile dropped into a worried expression as he turned and headed back to the dorms. He arrived quickly, rushing up the stairs to get there as soon as possible. There were soft sniffles coming from Uraraka's room, and he hesitated for a moment before rapping his knuckles on the door, causing the quiet crying to immediately cease.
“Momo-chan, I'm okay, really!” Her voice was strained and unsteady. “You don't have to-”
“It's Midoriya,” he called back to her, “May I come in?”
“U-uh-” There was some fumbling from inside, before she sighed in resignation. “Yeah, come in.”
He slowly pushed open the door, eyes widening in surprise. All sorts of small objects were floating in the air at varying heights. Uraraka was sitting stiffly on the edge of her bed, rubbing hopelessly at her teary cheeks as she sniffled a bit more. Mascara had trailed down her face and smudged around her lashes. She kept her gaze firmly on the carpet, even as he sat next to her on the mattress.
“What's wrong?” He asked softly, looping an arm over her shoulders and gently tugging her until she went slack and leaned into him.
“I-it's nothing, really, I just...” She sighed raggedly again, reaching out to clasp at his blazer, only to clench her hand into a fist and press it into her lap. “I miss my parents a lot, and school is becoming so stressful, and I just want... I just want some peace and quiet for once without villains attacking us again. And- and because I'm so upset I can't control my Quirk properly, hence...” She gestured vaguely at the hovering items. “And I was trying to apply my make-up but everything kept floating away, and I got so frustrated that I started crying and couldn't stop. I know, it's stupid- you don't need to worry about me, Deku-kun. I'm fine, really.”
He hummed doubtfully, squeezing her shoulder. “Well, the weekend is coming up - maybe you could catch a train and visit your parents. O-or... You could video call them, show them around the dorms, or something like that.”
Uraraka peered up at him with wonder in her eyes. “That's such a good idea! I could introduce them to all our classmates, too! Oh, they'd love that, I'm sure!” She giggled, pressing her face into the side of his chest. “I can't believe I didn't think of that, I'm so silly.”
He huffed in amusement, glad to have brought back her sunshine-smile. “For now, I could help you with your make-up- a-ah, if you want, that is! I can just leave if you-”
“You can do make-up?!” She pulled away from the loose embrace to gaze at him, wide-eyed.
Izuku nodded, already feeling his cheeks heat up again with his embarrassment. He reached up and snatched make-up wipes from the air, pulling one out and raising it to her face uncertainly. She closed her eyes and leaned closer to him, and he gently started swiping away the ruined mascara until her skin was clear once more. He was quick to brush and blend, lightly contouring her cheeks and delicately winging her eyeliner until she looked like a goddess.
Uraraka grabbed a mirror, staring at herself with awe. “I look amazing, thank you so much! Where did you even learn how to do this?”
He combed his fingers through his hair, awkwardly looking at a wall to try and lessen his embarrassment. “I watched some tutorials and practised on myself and my mum.”
“On yourself...” She mumbled, before lighting up. “Can I do your make-up, then?”
“Uh, yeah, okay!”
It didn't take long for the two of them to make their way to class, playfully holding hands and swinging them between the pair with every step. Uraraka had her bounce back, and she was hopping excitedly, practically dragging the boy along in her restless desperation to show off their make-up. She enthusiastically shoved open the massive door to their homeroom, effectively garnering all attention. Izuku half wanted to floor to have a quicksand Quirk so he didn't have to face all his stunned classmates, but when he noticed Yaoyorozu's grateful smile he couldn't help but grin back.
“You look incredible, Uraraka-chan!” Ashido exclaimed delightedly, leaping off her desk and rushing towards them. “Oh, you too, Midoriya-kun!”
“Thank you,” he said with a soft laugh.
“Deku-kun did my make-up!” Uraraka exclaimed gleefully, causing more eyes to widen. “Isn't he talented?”
“Really?” Yaoyorozu stood up, an earnest expression of interest dancing on her features. “Would you mind doing mine sometime, Midoriya-kun?”
“O-oh, sure! That sounds great-”
“You're both very pretty,” Aizawa drawled as he dragged himself into the classroom, and – was that a hint of a smile?! “Please sit down and don't disrupt my class any further.”
“I'm telling you, bro, that tiny bird ate an entire hot-dog!” Kirishima insisted, bumping his shoulder against Iida's as they walked through the dorms.
“It just doesn't seem possible.” Iida shook his head with a doubtful look.
“You just don't appreciate my stories, I understand.” The red-haired boy clenched a fist melodramatically, sounding heartbroken, but he quickly perked up and paused in front of a door. “Wait, I know who'll appreciate me-” He knocked on the door, not pausing before shoving it open and stepping inside the dark bedroom. “Yo, Midoriy- a...” He trailed off, dumbfounded.
There was a girl sitting on the bed. A girl in a familiar All Might hoodie. A girl with freckles and messy green hair. A girl that had gone bright red and attempted to dive under her blankets, but it was too late – she was doomed.
“...what...?” Iida mumbled, stepping forwards as if to approach before he seemed to think better of it and stayed by the door.
“Uh... Dude... -ette? What's... what...” Kirishima could only stare gormlessly, entirely bewildered by the unexpected turn of events.
The girl tried to become one with her hoodie, sinking down inside it and pulling the hood over her face. “Hi, guys...”
“You're... Midoriya-kun, right?” Iida asked uncertainly, partially wondering if this was some kind of intruder and getting ready to bolt out of there to alert his teachers; the girl nodded faintly. “And you're... a girl?”
“I was hoping this wouldn't happen, but... I guess I'd better explain... Kirishima-kun, could you shut the door, please?” Izuku sighed in resignation, sliding to the edge of the bed to stand up. “Well, uh... My Quirk allows me to, um... change from male to female...?”
“Your Quirk- I thought you had a strength enhancement Quirk? You have a secret Quirk?!” Kirishima was already freaking out, torn between excitement and confusion.
Izuku tugged off the large hoodie, leaving her in shorts and a t-shirt that revealed her subtle figure. Both boys were stunned silent, and she winced at their reactions. She concentrated on her Quirk, feeling her bones shift as her hips slimmed and watching as the shirt loosened around her chest, returning him to male form.
“That's... remarkable,” Iida finally said, before a frown creased his face. “How come we didn't know about this?”
“Only my mum knows.” He shrugged helplessly, rubbing a hand over the scars on his arm. “I just... wanted to keep it a secret, because I wasn't sure how people would react.”
Kirishima closed the distance between them, crushing the boy in a manly hug. “Dude, thank you for sharing this with us. We love you, okay?”
Izuku huffed with laughter, secretly glowing with relief. “Yeah, yeah... I know. Love you too.”
“I presume you want us to keep this a secret from everyone?” Iida inquired carefully. “You're going to have to tell them eventually, though.”
“Y-yeah, but... Not right now.” He sat back down on his bed, staring at the floor nervously.
“We'll be there when you do to help you, bro,” Kirishima immediately reassured, patting his friend's shoulder.
Iida nodded in agreement. “Yes- I am curious, though. Is there anything else that Quirk can do?”
Izuku instantly lit up, as eager as ever to ramble about Quirks to his friends.
When Aizawa had tiredly announced a class trip, everyone had been ecstatic.
At least, they were until the bus was stopped by villains who were, for some ungodly reason, lurking around a road in the middle of literally nowhere. There were so many bad guys that it almost seemed as if they had interrupted some kind of villain convention, which Izuku considered once more as he ducked under another punch that shattered the concrete.
The amount of villains with a mutant-type Quirk made it difficult for Aizawa to be immensely effective, and the students with better physical capabilities, like Satou and Kirishima, took it upon themselves to take them on to ease his burden. Everyone was giving it everything they had, and the strain was starting to show as they kept getting hit by blows they should've been able to dodge.
Izuku winced as he spun around, feeling the jagged cut across his torso from a villain with a blade Quirk pull unpleasantly. He leapt up, bringing his feet down on the enemy's skull and knocking her unconscious, but there was no time to breathe when his friends were all struggling. With the help of Full Cowl, he was able to rush over to Aoyama and defend him by kicking the villain in the gut before he could bring down a chain on Izuku's eccentric classmate.
The green-haired boy glanced around to take stock of the situation. Over half of the villains were knocked out, sprawled across the ground and hastily stuck down with Mineta's and Sero's Quirks, but the ones that remained standing were clearly the strongest. Izuku was slowing down unintentionally as the exhaustion was catching up to him, every move burdened with pain so bad not even adrenaline could cancel it out. There was an idea starting to form in his mind, but he was reluctant to use it unless it was absolutely necessary.
He sidestepped to allow Aoyama to shoot his navel laser, successfully blasting away the villain. Izuku couldn't spare another moment to check if things were fine, already forcing his aching body across the impromptu battlefield to provide much-needed back-up to Kouda, who could only do so much without his animals. His mind was blank, the only thought keeping him going was help. No Pro Heroes would be venturing out so far, so they had to hold their own and they had to win.
He darted around villains and threw brutal attacks, fighting back-to-back with his friends and working in tandem to take down enemies. There was a scream that distracted him enough to turn his head, which was a mistake. Something slammed into the side of his skull with the force of an obsidian mallet, blacking out his vision and sending him crashing to the ground.
His head pounded. It almost felt like he was floating. Warmth trickled down the side of his face and a metallic taste stung his tongue. His jaw burned in agony, and gritting his teeth only made it worse.
Izuku blinked open his bleary eyes. The light only made his headache worse, but he needed to push through. There was a large figure looming over him, blurred around the edges. He squinted, not sure if the person was violently spinning or whether it was just his vision.
Move, his instincts screamed at him. A vague shape was careening down towards him. Move. He needed to move-
Wide, grey straps wrapped around the villain's body, tugging him back. Izuku stared in surprise before following the tendrils of fabric, spotting Aizawa restricting the enemy from killing his student. The boy's breath caught in his throat as he saw villains sneaking up on his teacher, whose sole focus was to protect.
Izuku heaved in a breath and focused on his secret Quirk, almost sighing with relief as the agony faded into a dull thrum in the background. There was no point in pride if he was dead.
She shot to her feet, revelling in her newfound energy, and slammed a steel-toed boot into the villain's chin, causing him to immediately crumple. The straps loosened and released, springing back to their owner with Izuku in tow. She threw her whole bodyweight at a large villain, tackling him into the dust and slamming his head into the earth until he fell still, but she wasn't done there.
Two villains remained, still fighting with all they had despite the odds. She sprinted past one, jabbing an elbow into his ribs to give Aizawa an advantage, before bounding towards the other one, which she had identified as having a Quirk that allows them to do more damage the more pain they're in. Kacchan and Kirishima were working together, setting off explosions and landing sharp hits that only made things worse for themselves, not that they seemed to realise it.
The redhead got caught in an unexpected backhand swing, barely able to harden before he hit the ground, dazed. Kacchan only snarled louder, dodging a slap and trying to get close, only to be crushed into the ground. Izuku shot forward, green lightning winding around her body and snapping angrily, and she flung herself into the fray with a chilling, animalistic screech. She may have been small in comparison to the villain, but the force behind her attack sent them crumbling down like a sandcastle, unable to even think about retaliating before she shoved her foot at their skull.
Izuku stood there for a moment, chest heaving as she glowered down at her victim.
The reality of what had just happened hit her with the force of a speeding truck, and she tried her best to shrink in on herself before slowly turning to face her classmates.
And, oh, if those perplexed looks weren't aimed at her, she would've laughed.
“I fucking had that villain, Deku,” Kacchan growled, although it seemed to lack its usual bite. “You didn't need to fucking show off.”
Izuku decided that it wasn't the time to point out that he would've been dead without her, and instead nodded mutely. A friendly handed patted her on the shoulder and she glanced up at Kirishima, who was grinning at her supportively.
“Deku-kun...” Uraraka started, approaching her with obvious hesitance. “Um... what happened to you?”
“Was it a villain's Quirk?! Are you stuck as a girl forever now?” Ashido called over, looking surprisingly excited by the prospect.
“A-ah, no, it's not...” She frantically waved her arms, stumbling over her words.
Aizawa was suddenly by her side, staring suspiciously at the side of her head. “Midoriya, are you injured?”
“Not... in this form,” she answered carefully.
He looked at her for a moment longer before sighing roughly and turning around. “I'm not paid enough for this... Alright, everyone back on the bus.”
The class rapidly regrouped, all taking their seats and immediately clamouring for Izuku's attention, asking a thousand questions a second. She was quick to spill the whole explanation under Aizawa's intense stare. Despite Iida and Kirishima taking it all so well, she was still clenching her hands into painfully tight fists and gazing nervously at her lap by the end of the story.
“I wish I had a Quirk like that,” Mineta said hoarsely; Aizawa's capture weapon mysteriously gained a mind of its own and smacked the pervert to the floor.
“Though his intentions are wrong, I do have to agree with Mineta in that it's a very interesting Quirk, Midoriya-kun.” Yaoyorozu admitted with a reassuring smile.
“You know, you sometimes being a girl explains a lot,” Tsu mused, one finger on her chin; most people nodded in agreement, and Izuku flushed bright red, laughing sheepishly.
“Can you show us?” Ashido inquired eagerly, bouncing in her seat as she eyed her friend.
“Not right now,” she responded with a timid shake of her head. “My male form is badly injured and, uh, well... I'd probably pass out the moment I changed.”
“You're going to have to face some punishments for keeping this a secret, Midoriya,” Aizawa said lowly.
“They thought I was lying when I tried to register it because I couldn't control it yet,” Izuku mumbled, playing with her bloodied gloves and staring at her lap. “S-so I didn't try again.”
The teacher frowned, letting out a quiet, frustrated noise. “I'll talk to Nedzu about fixing it.”
Izuku nodded thankfully, relieved that she wasn't going to get in trouble. All her friends had accepted her, and she couldn't be happier.