Archive of Our Own ^beta

Chapter Text

The first time Izuku hears of the mysterious “Big brother ‘Toshi” it’s a random Monday morning. 

Izuku is minding his own business on his walk to class when a familiar voice shouts his name in the halls. Izuku halts in place, looking around for the source. 

“Deku!” Izuku hears Eri’s bright voice calls out for him once more. Izuku hears her before he sees her, but soon enough a small ball of long silver hair and red dress is bounding around the corner straight at him. Izuku watches in glee as Eri runs to him, Aizawa-Sensei just a few paces behind. Eri doesn’t fling herself at him, instead stopping right in front of him, breathing fast but smiling. Izuku kneels down to her height, noticing that she most likely didn’t tackle him because she’s clutching something in her hands. 

“I have something for you!” Eri proudly holds out a sheet of paper, thrusting it towards him. The enthusiasm warms Izuku’s chest; seeing how far she’s come always manages to make him a little misty-eyed.

Izuku takes the paper gently, Eri’s excitement fueling his own as he looks at it. It’s a drawing of him, of Deku, in all his hero costumed glory. His fist is raised in success, a huge smile on his face. Green swirls signify his hair, and the details of his costume are clear; the belt around his waist even has little squares to represent his pouches. The drawing is a little more put together than the ones she usually makes, but the care Eri clearly put into it is the same as always. Izuku’s heart soars looking it over. 

“Whoa, Eri this is amazing!” Izuku says genuinely. He’s not crying but it’s a near thing and no one can even blame him for it. “Thank you so much, I love it!"

“Big brother ‘Toshi helped me with it!” Eri tells him, voice pitching higher in her eagerness.

“Huh?” Izuku questions, head tilting as he tries to place the name. It’s not one he’s heard before in connection to Eri. “Who’s that?”

“Big brother ‘Toshi!” Eri repeats like it’s obvious and Izuku is being silly by playing dumb. “Aizawa’s son.”

Aizawa’s son, Izuku thinks, synapses firing a mile a minute. Aizawa has a son. Izuku looks up at the man in question. He’d come around the corner with Eri, of course he had, and he’s standing a bit behind the little girl to give them the illusion of privacy while still being close. Aizawa-Sensei raises a single eyebrow at Izuku, face void of any emotion. 

Izuku decides quickly it’s best not to ask. 

He thinks about it though.

Izuku doesn’t actually get much chance to think about the fact that Aizawa-Sensei apparently has a son. A son older than Eri. A son that Eri affectionately calls “Big brother ‘Toshi”. It’s driving Izuku crazy a little bit that that’s all the information he has. He doesn’t even know how much older than Eri this mysterious son is! Izuku doesn’t even know his full name because ‘Toshi is so clearly a nickname that Eri has taken to using. 

It’s killing him just a little bit. 

But, Izuku doesn’t have much time to wallow. He’s got his studies and his training to worry about, he doesn’t have much brainpower to devote to agonizing over Aizawa-Sensei’s mysterious son that Eri talked about so fondly that one time. 

(That’s a lie, Izuku thinks about it a lot. He can’t just ignore the biggest mystery of his life so far. Not when it’s been dropped into his lap, wrapped nicely in a bow. Aizawa-Sensei? Having a son? The fact is so incongruous with what Izuku already knows about Aizawa-Sensei that he can’t stop thinking about it. 

Is his son biological? Is he adopted? Was he rescued from somewhere like Eri? How old is he? Eri called him big brother, meaning he’s older, but by how much? One year? A few years? Or is he much older than her?

Izuku knows for a fact that Aizawa-Sensei is thirty years old. Mic-Sensei had burst into class with cupcakes and party poppers on the man’s birthday. If this son of Aizawa-Sensei’s is biological, Izuku assumes the boy is younger, probably around Eri’s age. Aizawa-Sensei seems too responsible to have caused a teen pregnancy. Izuku imagines that Aizawa-Sensei has always had a serious air about him, and would’ve taken his studies too seriously to risk something like that. 

So, a younger kid, maybe around ten? Unless the child was adopted or rescued in a similar fashion to Eri. That could make the kid any age.

Izuku’s got nothing, basically, and it drives him crazy to not be able to solve this mystery.)

But then, Eri comes to spend the night in the dorms with Class 1-A, and Izuku manages to get a little more information. 

Aizawa-Sensei explains that he’s been trying to give Eri as many “normal kid experiences” as possible. Eri doesn’t have friends her own age, she hasn’t been to a public school yet, so these experiences are being shared with adults or teenagers. Not ideal, but better than no experiences at all. Aizawa-Sensei also explains that Hound Dog is worried about Eri becoming too codependent, so they came up with the idea for Eri to have a sleepover. 

Being in the 1-A dorms seems like a good middle ground for her first sleepover. She’ll be out of the house and away from all its inhabitants, but still in a slightly familiar environment with people she trusts. A new experience, but should theoretically, be safe enough for her to not freak out. 

They plan it out at the beginning of the week, giving Eri time to get used to the idea that she’ll be spending the night out of the house, away from Aizawa-Sensei (and whoever else, because Izuku doesn’t actually know what Aizawa-Sensei’s immediate family entails and he’s only ever heard of big brother ‘Toshi. Does Aizawa-Sensei even have a significant other? A partner? Great, another mystery for Izuku to fixate on). Eri is nervous to be away from her family, to be away from the house she’s come to associate with safety. But knowing that she’ll be with 1-A and Izuku himself helps to calm her nerves. 

Friday night rolls around and Class 1-A is excited and prepared for Eri’s arrival. The common room floor has been turned into one giant bed; they’ve collected every spare mattress from the empty dorms, and every pillow and blanket anyone was willing to part with. The floor is waiting and ready for whoever wants to crash in the common room tonight in true sleepover fashion. Most of the class will probably end up falling asleep down here, with how determined everyone is to make this night perfect for Eri. 

At six in the evening, a knock rings through the room.

Eri and Aizawa-Sensei are standing in the entryway, slowly making their way inside. Aizawa-Sensei is holding her bags and what looks like a container of food. Aizawa-Sensei carefully guides Eri closer to Izuku until the three of them are standing in the space where the common room and the kitchen.

“I’m gonna go put this away, alright?” Aizawa-Sensei says to Eri, raising the container. Eri nods, shyly coming closer to Izuku. Aizawa quickly goes into the kitchen, returning the greetings the kids give him. 

Izuku turns his attention back to Eri, crouching in front of her so she doesn’t have to look up at him. It’s then he notices that she’s clutching two adorable plushies to her chest; the unicorn Izuku knows Aizawa got her not long after he took her in, and a cat. 

“Oh, you got a new stuffed animal!” Izuku comments, hoping to put her at ease and lower her shoulders from her ears. “It’s so cute!”

“Not new,” Eri corrects him. She holds it up proudly, though Izuku notes she keeps a solid grip on it. “It’s ‘Toshi’s! He said I could bring it with me tonight in case I get scared. He said it’ll make me feel extra better if I have both.”

“Oh,” Izuku hears some of his classmates cooing behind him. They all love Eri to pieces, even the ones who try to act above it all, and they all want to make her feel welcomed and safe. And they all appreciate it when others do the same. “That’s really nice of him!”

“Yeah, ‘Toshi’s the best,” Eri snuggles the little cat under her chin. It’s endlessly adorable, and Izuku almost coos audibly even though inside his brain is itching to know who the hell ‘Toshi is. Every new bit of information he gets from Eri makes him want to solve this mystery even more. 

He’s not the only one, evidently. 

“Who’s ‘Toshi, Eri?” Uraraka asks, crouching down next to Izuku in front of her. There’s mischief in her eyes, and Izuku is already resigning himself to her and Todoroki playing detective in the future. “I haven’t heard you mention him before.”

“Big brother ‘Toshi!” Eri says, excited for any opportunity to talk about her apparent big brother. Her smiles have been coming so much easier recently, and there’s a wide one now. Izuku’s heart melts at the sight, and it’s hard to be jealous of this mysterious big brother when Eri clearly loves him so much. 

“My son,” Aizawa cuts in with an explanation as he comes back from the kitchen. He kneels down beside Eri, her bag in hand. It should look comical, their scary teacher always clad in black, holding a pink and purple sparkly backpack. Eri’s shift in demeanor from happy to sad at the reminder of Aizawa leaving soon takes away any humor from the image. 

“He also packed that book he’s been reading to you,” Aizawa continues. “It’s here in your backpack. He said it’s alright if you have Midoriya read you some before bed if you want.”

Eri’s eyes are wide, and she looks both happy and apprehensive. “Oh, but I don’t want ‘Toshi to feel bad if I read it without him. Then I’ll be ahead and he won’t know what happens!”

God, Eri is so sweet it makes Izuku’s heart clench.

“He’s already read it, remember?” Aizawa-Sensei reminds her gently. “He read it first to make sure it wouldn’t scare you. And you know he’d rather you sleep than worry about that. You can always ask him to reread the parts with you.”

“Oh, okay,” Eri is clearly relieved at having a course of action now. Izuku marvels a bit at how easily Aizawa-Sensei was able to put her at ease. It makes sense, he’s had custody of Eri for a few months now, of course he knows how to calm her down. It’s still sweet to watch, though. 

“You have a son, Aizawa-Sensei?” Uraraka asks as soon as there’s a dip in conversation. Izuku looks around, noting that everyone in the common room is now paying attention. Maybe it shouldn’t be so surprising to them, Aizawa-Sensei is like, a full adult. He has a stable career, he’s super smart, and-- Izuku would never say this out loud, not even under threat of death-- he is kind of handsome. Regardless, it’s jarring to know that their teacher has a family. It sounds stupid to think of it like that, but Aizawa-Sensei rarely shares about himself. He’s a mystery to them and they eat up information about him as if they’re starving. 

“Yes,” Aizawa-Sensei answers. He’s trying to sound stern with them like he usually is, but there’s an undeniable softness that he can’t seem to rid himself of when talking about his family. Aizawa-Sensei doesn’t look at any of them, focusing instead on showing Eri what’s in her backpack. 

Uraraka is not deterred. She’s using her status as one of Aizawa-Sensei’s favorites to her advantage here. “How old is he?” She sounds innocent, but Izuku knows better. She’s going to be a menace about this later.

“High school,” Aizawa-Sensei zips Eri’s backpack, the quick zip! signaling the end of the conversation. Uraraka pouts, but she’s gotten more information than Izuku has thus far. She should be proud. Aizawa-Sensei hands the backpack to Eri, making sure she takes hold of it. 

(High school?! Izuku thinks hysterically. Our age?

If this son of his is biological, that means Aizawa-Sensei got someone pregnant when he was their age. The thought makes Izuku’s cheeks burn red. No, there’s no way. This son of Aizawa-Sensei’s must be adopted. They have to be.

High school. Izuku has an age now.)

“I’m gonna go now, okay?” Aizawa-Sensei’s voice is soft now that he’s totally focused on Eri. Eri gives a slight nod. It’s a tone that Izuku and the others only hear very rarely; when one of them is struggling mentally, be it nightmares or stress or plain old homesickness. Aizawa-Sensei is rarely gentle, but when he is, he’s earnest and true. Maybe that’s what makes it so comforting. 

“If you need anything, anything, Eri, ask Midoriya to call me. Even if you just want to say goodnight, you can call, okay?” 

“Okay.”

“And if you want to come home all you need to do is say. It doesn’t matter if the sun is still out or it’s the middle of the night. If you want to come home you can. No one will be upset or mad or disappointed, I promise.”

Eri looks comforted by the reassurances, not so nervous anymore. The grip on her backpack isn’t so tight that her little knuckles are white. “Alright.”

“Alright,” Aizawa-Sensei repeats and opens his arms for a hug that Eri eagerly falls into. 

“Love you,” Aizawa-Sensei kisses Eri’s forehead when she pulls away. It’s undeniably cute, but still a little trippy to see their strict teacher be so affectionate. “We’ll see you later, yeah?”

Eri nods again, more happily this time which is good. “Bye,” she says sweetly. 

“Bye,” and just like that, Aizawa-Sensei leaves the dorms with one last wave to Eri and the students. 

Later that night, Eri shyly asks Izuku to read to her before bedtime. Izuku reads one chapter of The Wizard of Oz, trying his best to be engaging and entertaining, but calm enough that Eri relaxes enough to fall asleep. Laying beside him, Eri fights off sleep to watch and make sure Izuku stows the book safely away in her bag. 

“What did you think?” Izuku whispers. “Did I live up to your big brother’s reading?”

Izuku is not jealous. He’s not. 

“‘Toshi reads better,” Eri says sleepily, snuggling into her blankets and clutching both of her plushies to her chest. She’s completely unaware of the damage she’s just dealt him. “Good night, Deku.”

“Good night,” Izuku says back on autopilot but Eri is already asleep. It’s just as well because Izuku can feel that his face is scrunched up and pinched. 

Izuku is not jealous. He’s not.

Kacchan cackles from across the room. 

Izuku means it this time when he says he doesn’t have the time to think about Aizawa-Sensei’s son and Eri’s big brother. 

It just becomes a part of his life now. Eri will casually mention her big brother ‘Toshi in ways that make Izuku burn with jealousy, and then the topic will change and Izuku never learns more about this mystifying teenager stealing Izuku’s title as Eri’s best big brother figure. Sure, the guy is actually her big brother; according to Eri ‘Toshi was with Aizawa-Sensei long before her, so he’s been her big brother the whole time. But still, it’s the principle of the thing. 

Izuku’s got this one-sided competition for best big brother and he doesn’t even know the other’s full name. 

Uraraka thinks it’s funny. Todoroki helps him gather evidence. Kacchan thinks it’s pathetic. 

(It is a little pathetic. Izuku won’t admit that though.)

Izuku forces himself to not dwell on it. It doesn’t do him any good to compare himself to someone when there’s nothing to compare. Izuku is one of Eri’s heroes. ‘Toshi is Eri’s big brother. They’re both important to her in different ways-- they’re both family in different ways. It doesn’t matter that big brother ‘Toshi reads her stories better, or teaches her how to draw, or promises his stuffed animals will keep her safe, or always peels the skin from whatever fruit she’s eating, or braids her hair, or lets Eri sneak into his room at night even though Aizawa has apparently told them to stop doing that because when he checks on Eri in the mornings he always freaks out to see her bed empty, or shares new foods with her so she doesn’t feel bad about wasting if she doesn’t like it, or always lets her pick the movie when it’s his turn on movie night, or-- 

Anyway. Izuku is not spending his precious time thinking about Eri’s big brother. 

Izuku has things to do, deadlines to meet, goals to accomplish. He doesn’t have the spare brainpower to devote to wallowing over Eri’s big brother. Especially when that thing to do, deadline to meet, and goal to accomplish is a research essay for Midnight-Sensei. 

Which is how Izuku finds himself in the library right after school searching the shelves for information on Impressionist art. Honestly, Izuku loves learning. He soaks up knowledge about any and everything like a sponge. He never turns down an opportunity to learn something new and he never will. 

But. 

There are only so many resources for Impressionism in the top hero school of Japan. 

It takes Izuku far too long to find the three books he wants, and by the time he gets to the front to check out the books, there’s a line. It seems the first-year class isn’t the only one that’s been assigned a research project, because Izuku recognizes the faces of three second-year hero course students, and two third-years. It must not even be just the hero course students either, because there are general education students in front of Izuku as well. 

Izuku lets out a soft sigh, preparing to be in this line for a while. He’s resigned to it, but he won’t be upset about it because the poor librarian is all alone at the desk and doing her best. Izuku is about to start leafing through one of his books to pass the time when it clicks in his brain just who is in line in front of him. 

Tall, lanky (actually, there’s more definition in his shoulders than the last time Izuku saw him), and purple. 

Shinsou. 

Izuku has attempted to talk to Shinsou a few times since their fight at the Sports Festival, and has succeeded a grand total of three times. They’ve been simple conversations; the first one was full of tension that Izuku had no hope of breaking until Shinsou had done it himself (“I thought I told you to win after beating me. That didn’t mean immediately losing in your next round.” “Well, sorry, I broke literally all of my fingers. It’s kinda hard to fight after that.” “Dude, what the fuck?”), the second just a quick hello, and the third when Izuku had been in front of him in the lunch line and asked about Shinsou’s plans for joining the hero course. 

(“Shinsou! Hi!” Izuku spun around so he could face Shinsou while Uraraka guided him forward in the line.

“Hello, Midoriya,” Shinsou kind of looked like he wanted to ditch the line to escape. He must have figured a quick conversation with Izuku was worth not skipping lunch, because he only looked a little annoyed. 

Well, now or never, Izuku thinks. Izuku thought Shinsou deserved to be a hero, deserved at least a chance. And if Shinsou didn’t have a plan to get into the hero course himself, Izuku was going to help him. But he needed to ask first. 

“I’ve actually been wanting to ask you something, if you don't mind,” Izuku says, trying to be as casual as possible but most likely missing by miles. 

“What would that be?” Shinsou asks, eyebrow raised. Almost like he didn’t expect Izuku to respond. As if. Izuku wasn’t afraid of Shinsou’s quirk, and he’d answer however many questions the other boy threw at him to prove it. 

“I wanted to know if you have a plan for entering the hero course,” Izuku without hesitation. He’s nervous to ask about such a touchy subject, but he can’t hesitate. Otherwise, Shinsou will think he’s hesitating to respond, and that just won’t do. Izuku is prepared to be rebuffed. Prepared for some of that sharp anger that was so present in Shinsou during the Sports Festival. Prepared to be sneered at as Shinsou leaves. 

That doesn’t happen.

“I have a plan, yeah,” Shinsou says easily, just a touch of suspicion behind his eyes. “I’m still working on it.”

“Really?!” Izuku can’t stop the excited exclamation. Izuku really, truly believes that Shinsou would make an amazing hero, if only he were given the chance to prove himself. “That’s amazing! Can you tell me? Is there anything I can help with?”

Shinsou is shocked, but he hides it well, his blank expression back on his face in just a few seconds. It saddens Izuku to see how guarded Shinsou is about his dream to be a hero. It reminds Izuku of himself in a way that makes his gut twist painfully and his eyes water. 

“I can’t tell you everything,” Shinsou says carefully. I won’t tell you everything. I can’t trust that. Izuku hears it and he understands it intimately. “It’s still kind of hush-hush. Just to be safe.”

Oh, that sounds a lot more official than Shinsou just working on his own toward his goal. That makes it sound like a done deal. Izuku can feel his curiosity growing, and he’s bouncing in place slightly in excitement. The rest of his friends are paying more attention now as well, and Shinsou eyes them warily, but he doesn’t shut down. Progress. 

“What can you tell me?” Izuku asks. He’s ready to beg, honestly. Shinsou must be able to tell because his lips twitch like he wants to smile. 

“I started a supervised training routine with some of the hero course teachers,” Shinsou says casually, like it’s no big deal. Izuku may as well be vibrating. “I’m not doing anything crazy, but it’ll help me not be so behind when I transfer in. Because I will.” 

There it is. That blaze of determination that had been in Shinsou’s eyes at the end of their fight. When he had promised Izuku that he would be the best hero they’d ever seen. That determination that means Shinsou will, no matter what. It makes Izuku excited. Makes Izuku want to drag him to the training grounds and see how much he’s improved. 

“Hell yeah!” Uraraka says, invigorated herself. Shinsou snorts. Progress. 

“Is that all?” Iida asks. “Not that it isn’t great! It’s just--”

“I know what you mean,” Shinsou saves Iida from his floundering. “Technically, I’m not supposed to have access to your coursework. ‘Cause, ya know, different departments. But Aizawa-Sensei and All Might-Sensei have been giving me the textbook work for Foundational Heroics and Ethics. And they’ve been testing me on it. I’m still catching up to where you are, but I won’t be behind when I transfer in.”

They invite Shinsou to eat lunch with them, and even though he declines to sit with his Gen. Ed. friends, Izuku still counts the whole interaction as a massive success.)

Izuku’s not sure he can call them friends yet, but they’re definitely acquaintances, and that’s a start!

And now is a perfect time to strike up a new conversation. 

“Shinsou!” Izuku tries to project as much enthusiasm as he can into his quiet voice. He’s not whispering-- they are near the entrance of the library-- but he’s certainly not about to use his usual volume. Shinsou turns around, surprise clear on his face. Izuku notes happily that the taller boy doesn’t look annoyed or put out by Izuku’s presence. Progress!  

“Hi, Midoriya,” Shinsou matches Izuku’s volume, neither of them willing to raise above a near whisper. 

“How have you been?” Izuku asks. “How’s your transfer going?” Okay, maybe Izuku is getting more and more excited the closer to the end of the year it gets. Surely the school is going to give Shinsou a definitive answer about his transfer soon. 

Shinsou grins, sharp and a little mean, one side of his mouth lifting more than the other. If not for the brightness of his eyes, the grin would look a little cruel. As is, Shinsou looks smug. It makes Izuku want to drag him to the training fields all over again. In a friendly way, of course. He doesn’t want to beat Shinsou up or anything. He just wants to witness firsthand the confidence behind that grin. 

“Good,” Shinsou says proudly. “I’ve caught up to your class in coursework. It was hard as hell, by the way, basically doing two departments' worth of work, but I did it. And I learned a new move last week.”

“Really?!” Izuku’s voice raises before he can stop his excitement. There’s a harsh sh! from the tables closest to the door, and Izuku flushes but his excitement doesn’t abate in the slightest.

“What kind of move?” Izuku asks quieter. If Izuku thought Shinsou’s grin was smug before, it pales in comparison to now. 

“You’ll just have to wait and see,” Shinsou teases. 

“No fair,” Izuku whines, but he’s not really that upset about it. The way Shinsou had said that sounds like a promise. Izuku will see his new moves. Because soon he’ll be in the hero course. 

As Uraraka would say, hell yeah.

Shinsour shrugs, unrepentant. They’ve been moving up in the line, and now there are only two people in front of them. Izuku was worried it would take much longer than this. 

“What are you getting?” Izuku asks, motioning to the single book in Shinsou’s hand. The other boy looks a little embarrassed all of a sudden, and a little closed off. Is he worried that Izuku will judge whatever book he’s picked out? Izuku would never, but Shinsou doesn’t know that, so instead he keeps his expression open and curious. 

“It’s ah, a collection of fairytales,” Shinsou shows off the cover for Izuku to examine. 

“Oh? Is it for a class?” Izuku wonders. The cover of the book is beautiful; a tree outlined in gold, surrounded by storm clouds. 

“No,” Shinsou says sheepishly, free hand going up to rub at the back of his neck. He seems to debate with himself for a moment before visibly shaking off whatever was holding him back. 

“My little sister has trouble sleeping sometimes,” Shinsou explains. “When she does I read to her. We just finished a book of American fairytales. This one is Japanese folktales. I haven’t had the time to go to the library in the city, so I thought I’d look here for a book and found this. Thought she might like it.”

Shinsou’s voice goes all soft and fond talking about his little sister, and Izuku feels his heart warm. Shinsou so often looks so serious and tough, it feels like a treat to see a softer side of him. 

“Ah, that’s so sweet, Shinsou! I hope she likes them!” Izuku says genuinely. He’s also hauntingly familiar with the inability to sleep, Shinsou’s little sister is lucky to have someone to turn to on hard nights. 

“I’ll have to read them first to make sure they won’t scare her,” Shinsou says offhandedly. “She’s young, and she’s had a… rough go of things. The stories are supposed to make her feel better, not worse.”

“Oh,” Izuku says softly. That twists at Izuku’s heart, too. He can only imagine what happened to her to put that forlorn look on Shinsou’s face. Little kids shouldn’t have rough lives. But Izuku knows as well as anyone that the world isn’t fair. “That’s very thoughtful, Shinsou.”

Shinsou shrugs, brushing off the conversation. Shinsou is next in line, and he angles his body to keep an eye out while not closing himself off from Izuku. It’s nice. “What are you getting?” Shinsou gestures to the stack of books in Izuku’s arms. 

“Oh! They’re books for a research essay for Midnight-Sensei. It’s about the Impressionism art movement. I’m surprised I found this many books, honestly.”

“Ah, I’ve heard people complaining about this project,” Shinsou comments. It’s his turn in line, and it goes quickly with only one book. Izuku sort of expects Shinsou to leave after he’s finished, and he’s pleasantly surprised when Shinsou steps to the side to wait for Izuku to finish. 

Progress.

They walk out of the library together, chatting about their classes as they walk toward the dorms. It’s easy conversation that should maybe be boring, but Izuku is too ecstatic about Shinsou actively continuing their conversation to think it mundane. This is the longest they’ve spoken, and the small talk is welcome after the more personal turn things took inside the library. 

They have to part ways once they get to the dorms, the General Ed. dorms are in a slightly different direction. Their goodbyes are easy, and Shinsou even graces Izuku with a small smile when they part ways. It’s gentler than the sharp grin he usually gives people. 

Progress. Izuku thinks they might have just leveled up from acquaintances to friends. 

Two weeks later, Eri comes to spend the night in the dorms again. Their first try had been a success, and Eri’s had a good enough week that she was the one to suggest it. Class 1-A had readily agreed, excited to have Eri back (and they’ll take any excuse to host giant sleepovers with the whole class). Aizawa-Sensei hardly takes any cajoling to convince; he’s just as whipped for Eri as the rest of them. 

Eri asks him to read to her before bed again. Izuku is already preparing himself for another blow to his self-esteem and to feel irrationally jealous. Kacchan is already snickering because he’s the worst. Izuku puts on a brave face, because he’ll die before he denies Eri such a simple request. 

When Eri pulls out a familiar-looking book when it’s time for bed, Izuku feels himself freeze. His mind is blank, no thoughts running through his head. Eri doesn’t notice, holding the book out to him. He takes it on autopilot, and in Izuku’s hands is a Japanese folktale collection, the cover a stylized golden tree in the middle of a storm. 

No way.

“Big brother ‘Toshi says that all the stories are okay for me to read,” Eri announces proudly. “So you can pick whichever one you want, Deku!”

Big brother ‘Toshi.

Shinsou Hitoshi.

No. Way.

Izuku’s just solved the biggest mystery he’s ever seen. And all because of a storybook.

Izuku is going to have words with Shinsou come Monday. 

As soon as the lunch bell rings, Izuku is out of his seat and running from the classroom. He doesn’t even pause to offer his friends an excuse or explanation. They’re used to his odd behavior by now, they’ll survive one lunch without him. 

Izuku makes it the Generel Ed. classroom in record time. Only a few people have left, and when Izuku pokes his head into the classroom, he spies Shinsou’s bold purple hair. Good, he hasn’t left yet. 

“Shinsou!” Izuku calls. The boy in question looks up from where he’s packing his bag. The confusion is clear on his face when he sees it’s Izuku that’s called him. Izuku waves brightly. 

“Have lunch with me?” Izuku asks before the other boy can open his mouth. 

“Sure?” Shinsou responds, but it comes out like a question with the confusion he must be feeling. Some of Shinsou’s classmates pout and whine about Izuku stealing what little time they have with Shinsou, and like. Izuku gets it, he does, but if he doesn’t talk to Shinsou immediately Izuku might just die. Shinsou must see some of his desperateness, because he grabs his things and follows Izuku out of the building quickly. 

Izuku leads them outside and around the back of the main gym. There are some benches and tables back here, but the space is rarely used during lunch because it’s so far away from the cafeteria and there are no good vending machines over here. Shinsou doesn’t protest, doesn’t even say anything until they make it to their destination, and are sitting across from each other at one of the tables. 

“Is everything alright, Midoriya?” Shinsou asks, concern palpable. Izuku feels a little bad for freaking him out, but Izuku is freaking out, so. Turnabout is fair play. 

“Everything’s fine,” Izuku assures. Thinks. “I think,” he amends. 

Izuku is sure he’s sitting on information he’s not supposed to have. There must be a reason no one knows that Shinsou is Aizawa-Sensei’s son. For Shinsou’s safety probably. There must be plenty of criminals out there that would love to get revenge on the hero Eraserhead. Not to mention what the League of Villains might do if they ever learn that Aizawa-Sensei has a son. Eraserhead has come too close to beating them or capturing them for them to not use that information for bad. 

“You think? ” 

“Well,” Izuku flounders for a second. “I’m not even sure I’m right! I mean, I’m at least ninety percent certain. Really the margin for error here is minuscule, so I’m confident I’m right. But there are so many factors that I might be wrong. Coincidences are a thing, but there are too many to just be coincidence. And when you put it all together it does make a lot of sense. Maybe not the biological thing, I’m not as conspiracy driven as Todoroki. But then again, I suppose your quirks could be similar--”

“Midoriya, what are you talking about?” Shinsou interrupts. Izuku laughs nervously. Shinsou doesn’t look angry, just confused, so that’s a good thing. For now, at least. 

“Um, I brought lunch for us,” Izuku says, changing topics entirely. Shinsou looks flabbergasted. It’s a strange expression to be on his usually stoic face. “In case this takes a while and you didn’t bring anything for yourself. I don’t want you to go without lunch!”

Izuku is pulling two bentos from his bag as he speaks. He pushes one to Shinsou, who takes it out of reflex. He still looks dumbfounded. Izuku watches as Shinsou takes a deep breath, holds it for five seconds, and releases it slowly. Great, now Izuku’s got him doing breathing exercises. 

“Okay,” Shinsou says. “Thanks for the bento. Now tell me what’s got you so fired up that apparently has something to do with me.”

Izuku wants to curl into himself, that old self-doubt returning under Shinsou’s gaze. Really, this is none of Izuku’s business. He doesn’t have any right to the information he’s about to ask for. He should leave well enough alone, be content with thinking he knows the answer, and keep it to himself. 

But he’s already here. And Izuku thinks if he tells Shinsou to just forget it, Izuku will end up brainwashed and he wouldn’t even fault Shinsou for it. 

So Izuku plucks up his courage because if he’s going to be extremely nosey, the least he can do is look Shinsou in the eyes while he attempts to pry into his personal life. 

“I have a personal question to ask you,” Izuku prefaces before anything else. Shinsou’s face immediately goes closed off. That blank, stoic expression back in a second. There isn’t even any identifiable emotion in his eyes that Izuku can see. Shit.  

“And what would that be?” Shinsou asks, eyebrow raised sardonically. Izuku doesn’t think Shinsou will brainwash him right now, but the threat of it is there. He could if he wanted to, Izuku knows he could if he wanted to. 

But Shinsou won’t. So Izuku answers.  

“Are you Aizawa-Sensei’s son that Eri is always talking about?” Izuku asks, no longer beating around the bush. 

Shinsou blinks, his guarded expression falling away first to shock and then panic. 

Shit.

“I really shouldn’t have asked that!” Izuku immediately backtracks. “Just forget I asked! I obviously don’t know what I’m talking about! And even if I were right, it’s none of my business! I’m really sorry, Shinsou, I shouldn’t have asked--”

Shinsou raises a hand in the universal signal to slow down, and Izuku cuts himself off with a wince. Stupid, Izuku, he scolds himself. Why did you just do that?

“Um,” Shinsou looks at a loss for words. Great job, Izuku. You made the guy whose quirk relies on talking speechless. 

“Um,” Shinsou tries again. Izuku winces once more. “I don’t really-- How did you-- Oh.”

“Oh?” Izuku repeats cautiously. He’s never heard Shinsou stutter or stumble over his words like this. It makes Izuku feel terrible. 

“The book,” Shinsou says. “Eri’s book. I didn’t even think about that when I packed it in her bag for her sleepover.”

Izuku shifts uncomfortably, the table suddenly much harder under him. He opens his mouth to… say something. He’s not sure what. Thankfully Shinsou beats him to it. 

“I wondered if you might figure it out,” Shinsou muses. “I wasn’t going to say as much as I did in the library. Aizawa tells us to really cautious about stuff like that. It’s dangerous for people to find out, ya know?”

“Oh,” Izuku says softly. He figured there was a safety aspect to this as well. Izuku just didn’t really want that confirmed. It makes anxiety boil hot in his belly. 

“But,” Shinsou continues. “I mean. You’re a good person, Midoriya. I don’t think he’d be too worried over you knowing. Even if I didn’t think you’d figure it out just from a book.”

Crap, Izuku might cry right now. Shinsou said that so plainly, so simply. As if it were a fact that he believes Izuku to be a good person. A trustworthy enough person to hold such a personal secret. Shinsou continues talking, either oblivious to or ignoring Izuku’s misting eyes. 

“You would’ve either figured it out or been told eventually, I think,” Shinsou says. “I mean, you’re practically Eri’s honorary brother. You saved her. You’re her hero. Eri trusts you, and Aizawa has never tried to lessen how much faith she has in you, so it must be deserved.”

“Shinsou, you’ve gotta stop that, I’m gonna cry,” Izuku warns, voice watery. “You can’t just go on about how Eri trusts me like that and expect me to be okay.”

Shinsou laughs. Just once, a bark more than anything, but it’s the first laughter Izuku’s ever heard from him. A tear falls and Izuku can’t even find it in himself to be embarrassed. 

Shinsou graciously allows Izuku to pull himself together before dropping the lighthearted mood completely. 

“You really can’t tell anyone,” Shinsou says seriously. Izuku gets serious himself. “I meant it when I said it’s dangerous. There are plenty of people out there who would love to hurt Eraserhead by going after his family. I know I’m trying to get into the hero course and everything, but the fact is I’m not yet. I’m not a match for a villain with a grudge. And Eri… god, I don’t even want to think about what it would be like if someone with a bone to pick found out that Eraserhead has a six-year-old daughter.”

Dread floods cold through Izuku. He’d thought, of course, about safety being the main reason for secrecy. Eraserhead is an Underground Hero for a reason. No one knows Eraserhead’s real name. People hardly even know Eraserhead exists. He may as well be a myth for all the information available about him. He deals with the worst of the worst and he’s one of the best at doing it. Of course he has enemies. 

Hearing it from Shinsou, from Aizawa-Sensei’s son, puts it in stark relief. 

“I won’t tell,” Izuku promises. “I would never, I swear. I wasn’t even going to ask, but—“

“But you’re a nerd,” Shinsou says. “You like to know things. You figured it out and needed to be sure.” 

“Well, when you say it like that …” 

Shinsou snorts. “We’ll still have to tell Aizawa you know. That’ll be a fun conversation. But things will be fine. I think.” 

“You think,” Izuku repeats, swallowing harshly. Dread settles more firmly in his stomach imagining the look Aizawa-Sensei will give him. Izuku shudders. Shinsou’s grin is back to that sharp, kind of mean one. He’s back to himself then. 

“He’s definitely gonna scare you,” Shinsou says easily. “But you’ll be fine. Probably.”

“Probably? ”

“Relax,” Shinsou rolls his eyes and opens the bento box, making a pleased noise as he examines the contents. “He’ll lecture you, a lot. Might threaten you a bit. Aizawa likes his privacy, and you just figured out his second biggest kept secret. But you’ll be fine. He likes you.”

“Oh,” Izuku says, much happier this time. Pride is rushing through him at hearing his teacher likes him. Aizawa-Sensei likes him. Izuku’s going to ride this high for the rest of the week. He digs into his own bento. Izuku’s not sure how much of lunch is left, but it can’t be much. 

“Wait,” Izuku says, swallowing a bite of rice harshly. “His second biggest secret?”

Shinsou snorts again. “Good luck with that one. I’m not spilling anything.”

“Oh, come on!”

“No chance.”

Izuku lets it go. They eat their lunches in silence. Shinsou doesn’t have any complaints about the bento, even thanks Izuku again after he’s taken a few bites. It makes Izuku feel accomplished. He might have just given Shinsou the fright of his life, but he also gave him a good lunch. Life’s about balance and all that. 

Of course, he opens his big mouth again and ruins that. 

“You call him Aizawa,” Izuku says when their conversation has settled. “Is that… habit from school, or…” 

“I’m adopted,” Shinsou answers with forced casualty. It’s a sore subject, clearly, and it’s one that Izuku knows better to pursue. He’s dug into Shinsou’s life enough for one afternoon, and they’re not even really friends. Not close enough for Midoriya to have earned the story behind that. He won’t ask. 

Izuku nods, matching the casual air Shinsou is trying for. “Is it bad I’m a bit relieved about that? If you were his biological son that would have to mean that he’d gotten someone pregnant when he was our age .”

Shinsou laughs again, this one a real laugh. He’s put his chopsticks down, head thrown back in bright glee. Izuku doesn’t know why what he’s said is so funny, but Shinsou is properly in his laughing fit now. 

“Shinsou,” Izuku whines. “Why was that so funny?”

Shinsou doesn’t answer, just keeps snickering to his heart's content. 

“Come on, Shinsou,” Izuku tries again. “Tell me.”

“It’s nothing,” Shinsou chokes out, coughing as he tries to get himself under control. 

“Shinsou,” Izuku whines again, dragging out his name. 

“Holy shit,” Shinsou wipes at his eyes. Sure enough, tears had gathered during his bout of laughter. “It’s nothing. Can’t tell you.”

Izuku pouts, but he’s just glad Shinsou is laughing and that guarded, scared look is gone from his eyes. He’ll take the laughter over that any day. 

They finish their lunch with no more earthshattering revelations. Their small talk comes easily, both of them staying on lighter topics. Though Shinsou does grace Izuku with a few stories of Eri at home and Izuku basks in it. 

“You know,” Izuku says when they’re gathering their stuff to head back to the main building. “I was super jealous of you whenever Eri would talk about you. I didn’t know it was you, of course, but…”

“What?” Shinsou asks incredulously. “No way.”

“Yes, ” Izuku insists. “It’s always ‘Big brother ‘Toshi helped me with this.’ or ‘Big brother ‘Toshi does it this way.’ ‘Toshi does that better.’ It was driving me crazy!”

Shinsou looks like he doesn’t fully believe him, but his cheeks are a little pink. “I was jealous of you, too.”

“Huh?” Izuku whirls on him. “Why?”

“You’re her hero, Midoriya,” Shinsou says simply with a shrug. “You saved her. How was I supposed to compare to that? She talks about you all the time, like you’re larger than life. And to her you kind of are, you know? Like I didn’t see you snort milk out of your nose during lunch last week,” Shinsou scoffs. 

“Hey, that was not my fault. Blame Todoroki,” Izuku defends. “Are you still?”

“Still what?”

“... Jealous?”

“No,” Shinsou says after a moment. “It’s different, right? We don’t need to compare, we’re not comparable. We’re different people; in general, and to Eri. There’s no need to be. Are you?”

“Definitely not,” Izuku says quickly. Too quickly. Shinsou smirks at him. Izuku nudges their shoulders together. 

“I just don’t know why your bedtime reading is so much better!” Izuku complains. “I try!”

Shinsou lets loose another one of those full laughs, bright and happy. Izuku’s still proud of making Shinsou laugh like that. “It’s okay. You can’t be good at everything, Midoriya. Leave the storytelling to me.”

“Whatever,” Izuku rolls his eyes but he’s smiling now, too. 

Izuku doesn’t know how he’s going to look at Aizawa-Sensei during class now that he knows such for sure such personal information about him. Izuku doesn’t know if he’ll survive when Shinsou tells Aizawa-Sensei that he knows. Izuku doesn’t know if he and Shinsou will keep up this easy banter between them, or if they’ll go back to hardly speaking. 

But right now Izuku feels good. 

Chapter Text

“I’m gathering all the known evidence about Aizawa-Sensei’s son,” Todoroki tells Izuku after Eri has left the dorms. 

Eri had left their sleepover a few hours ago. Aizawa-Sensei had come to pick her up, mentioning that they had plans to go pick up lunch because Toshi’s been stressed, so we’re gonna go get the gyoza he likes, okay? Eri had been ecstatic to be on a mission to cheer up her big brother, cheering and hurriedly packing her things so they could go, go, come on, big brother ‘Toshi needs us! It was adorable and very sweet, and Izuku was only a little jealous to watch how eager she was to leave. 

Izuku knows where this is going with Todoroki, however. Izuku sighs, “And why are you doing that, Todoroki?”

Todoroki, because he knows his conspiracy tendencies drive Izuku to the brink, smirks. “You know.”

Izuku closes his eyes and takes a deep breath. Uraraka and Ashido are giggling off to the side, probably eager to help Todoroki themselves. “Fine. I’ll tell you what I know, but if we get in trouble for prying into Aizawa-Sensei’s life, we meet in Ground Beta and I’m kicking your ass.”

“You can try,” Todoroki shrugs. The girls giggle more. Izuku narrows his eyes. Oh, he’s definitely kicking Todoroki’s ass now. “Now, let’s go over what we know.”

Izuku sighs again but resigns himself to his fate. 

“So, to recap,” Todoroki says to the group gathered in the common room. Izuku is surprised that a majority of the class is here, but he guesses he shouldn’t be. They’re all deadly curious to learn more about Aizawa-Sensei. Izuku doesn’t think everyone will try to figure it out like Todoroki will, but Izuku has the suspicion that this is going to be Todoroki’s most asked-after theory. 

“Midoriya first heard of this big brother a few weeks ago. Considering how much time Eri and Midoriya spend with each other and how close they are, it seems odd that Eri only spoke of him recently. That could imply that this big brother only became a member of the family recently--”

“Or that she just didn’t feel comfortable talking about her family casually,” Momo suggests. “I can imagine that, after everything she’s been through, she would be hesitant to speak openly about something as personal as family.”

Izuku and a few others nod. That makes sense. Izuku is sure that Eri has a difficult relationship with the concept of family. She had been abandoned by her mother and tortured by the man who was entrusted to care for her. That has to have given her some complicated feelings. 

“She also spoke about him easily,” Izuku reminds. “She thought I was playing dumb by not knowing who he was. She thought I knew him already.”

Todoroki gestures to Izuku. “Excellent point. That brings me to one of my preliminary theories. But first-- we continue. We now know that this big brother is our age-- in high school. Aizawa-Sensei was unclear about what year, but just by doing some basic math, the oldest he can be is sixteen.”

“Explain that,” Kaminari requests, hand waving in the air. “I don’t remember how old Aizawa- Sensei is exactly, but he’s in his thirties, right?”

“Aizawa-Sensei is thirty-years-old,” Momo reminds him. “If he has a sixteen-year-old, well, that means--”

“We’re assuming this kid is biological!” Izuku cuts in, cheeks already pinking at where Momo was heading. “What if he was adopted? Like Eri!”

“Why couldn’t he be biological?” Ashido asks. Izuku can see the moment she makes the connection for herself, her cheeks turning their own interesting shade. “If his son is in high school, he has to be at least fifteen or sixteen. That would mean Aizawa-Sensei had him at… oh. Oh, that’s really young to have a kid.”

“Oh, my god,” Kaminari grins wildly. “Aizawa-Sensei knocked someone up when he was our age!”

That gets met with loud objections and outcries of disgust. Various pillows and objects get thrown at Kaminari until he cries out apologies. 

“If we could get back on track,” Todoroki says blandly. Kaminari stays half-buried under his newly acquired pile of pillows. “Let’s keep both options open for now. We also don’t know if Aizawa-Sensei is married or not. He hasn’t mentioned a partner of any kind. But, I also don’t think it would be difficult for him to hide a marriage. Most Pros keep their names the same when they marry-- too difficult for branding purposes. That could also apply to Aizawa-Sensei, since his Underground work is very sensitive, he wouldn’t want it to track back to his family.”

“Should we be looking into this?” Jirou asks. “You just said-- Aizawa-Sensei does a lot of sensitive hero work. He must be keeping his family a secret for a reason. It’s gotta be super dangerous.”

That does the job of bringing the mood down. The twenty of them, more than any other first-year class, know the dangers of being a hero. They all know how risky and threatening this job is. They don’t know anything about Aizawa-Sensei, and that has to be on purpose. They know random things about all of their other teachers, little anecdotes, and likes or dislikes. But they’ve got nothing on Aizawa-Sensei. 

“Like,” Jirou continues. “If a bunch of kids can figure out who Aizawa-Sensei’s family is, what’s stopping villains from figuring it out.”

And the mood has been thoroughly tanked. Kaminari tosses a pillow at Jirou, who snatches it out of the air with viciousness. 

“I don’t think Aizawa-Sensei would have answered me if he really didn’t want us to know,” Uraraka offers. “He could have ignored me, or told me to drop it. And Eri is a very understanding kid, if Aizawa-Sensei had seriously told her not to talk about their family, I don’t think she would, even on accident. So Aizawa-Sensei must not have given her any rules about talking about them.”

“I guess,” Jirou allows. She turns a hard glare on Todoroki. “Still, you had better be careful about where you keep all this info and who and where you talk about it. Nothing leaves this dorm.”

They all agree to the terms. None of them wants to cause Aizawa-Sensei any harm. Despite how secretive he may be, they all know he cares about them. They know he pushes them so hard because he worries about them. They know he’s so strict because he wants them to become the best heroes they can be. 

“What was your first theory, Todoroki?” Hagakure asks. “You mentioned one earlier.”

“Oh,” Todoroki sits up straight. “Well, considering how Eri brought her big brother up the first time with Midoriya-- talking like he should already know-- I propose that he has met Aizawa-Sensei’s son. I think he goes to U.A.”

And they’re all off again. 

On Monday in Heroics, they just so happen to be doing one-on-one sparing matches. Even rarer, they get to choose their partners. Izuku spars against Uraraka once and Iida twice before he goes after Todoroki. A nice warmup, if you will. 

He kicks Todoroki’s ass. And because Izuku is nothing if not petty, when he holds out a hand to help Todoroki up, he uses the grip to pull Todoroki close and whispers, “What was that you said about how I can try to kick your ass?”

Todoroki’s jaw drops, because he’s just as dramatic as Izuku, and demands a rematch. And really, who is Izuku to deny him?

Izuku kicks his ass again.

Izuku occasionally brings tidbits of information he learns about big brother ‘Toshi to Todoroki. Like how Eri said he’d been with Aizawa-Sensei already when she showed up, how he helps her with her homework and reads to her all the time. How he spends a lot of time working out but always makes time for her. An interesting fact he learns is that whatever school he goes to has dorms, so she really only gets to see him on the weekends. 

“A dorm system, huh?” Todoroki says, jotting it down in his notebook. “Interesting.”

“Wouldn’t it be considered favoritism if his kid went to U.A., though?” Sero asks, leaning over Todoroki’s shoulder to peer at the notebook. Todoroki obligingly tilts it so Sero can see. 

“Not necessarily,” Iida explains. “The same argument could be made for Torodoki’s attendance at U.A., and mine for that matter. He still would have had to test in order to get in. It may be different if Aizawa-Sensei teaches him. Principal Nedzu most likely wouldn’t allow that.”

“I’m sure there are plenty of schools that have dorm systems,” Uraraka points out. “One of the backup schools I applied to did. I think it’s mostly specialized schools that do it. And I can’t imagine Aizawa-Sensei would push his kid to be a hero if they didn’t want to, considering how serious he is about who he allows to be his students.”

“All excellent points,” Todoroki admits. “More research is necessary.”

Izuku mostly stops paying attention to Todoroki’s investigation into Aizawa-Sensei’s son. He occasionally gives Todoroki a new piece of information, but none of it is identifying-- at least to Izuku. 

Izuku sure as hell starts paying attention again when Todoroki pulls him to his room one evening, not bothering to explain himself beyond “I have a theory.”

So now, Izuku is sitting at Todoroki’s desk, staring at the mess in front of him. 

Taking up a wall of Todoroki’s room is a wheeled corkboard. A large one. Pinned to the board is a mixture of notes, facts, theories, and people, all connected by string. It looks far too complex and far too unhinged for something like trying to figure out who Aizawa-Sensei’s son is. 

Todoroki is lecturing him, going over his latest theory and pointing to various pieces of information pinned to the board. Izuku honestly is only listening with half an ear, too confused over how Todoroki managed to put this together. How did he even have the time?

“I’m telling you,” Todoroki points viciously at the corkboard. Where did he even get a corkboard that large? “I’m telling you. It’s that purple kid from the Sports Festival you fought! Look at the evidence!”

“Todoroki, where did you get a corkboard like that?” Izuku asks bewildered. He feels like he’s stepped into the office of a detective on the brink of a breakdown. 

“Momo made it for me. That’s not important,” Todoroki waves a hand through the air. Izuku would argue that it is important. He’s going to have to talk to Momo later about this because this seems a little extreme. “Look at the evidence! Shinsou is Aizawa-Sensei’s son, I’m sure of it.”

What even-- Izuku shakes his head, not trying to understand how Todoroki jumped to this conclusion. 

“How? How did you even-- you know what, I’m not going to question it,” Izuku mumbles. 

“Just look,” Todoroki gestures to the board again. “They even look similar!”

Todoroki is pointing at a particular section of the board, where he has Shinsou’s school ID picture, and an old yearbook picture of Aizawa-Sensei pinned next to each other. Izuku supposes he can see some similarities, buts that’s mostly due to the fact that both of them look tired. Mental quirks tend to exhaust anyone who has them, however, so that’s not exactly hard evidence.

“Where did you even find a picture of Aizawa-Sensei from when he was in school?” Izuku asks. 

“I asked Midnight-Sensei where I could find one,” Todoroki shrugs. Izuku nods in acceptance. It figures Midnight-Sensei would be all too happy to help with that, she seems to delight in teasing Aizawa-Sensei. “It took a while, and I could only find this one, but I did it.”

“Wait, so--” Izuku gestures to the board. “Are you going off the theory that Shinsou is Aizawa-Sensei’s biological son? You’re comparing how they look.”

“Yes,” Todoroki says simply. Izuku thinks his brain bluescreens, automatically rejecting the train of thought. “Their quirks are similar enough. Erasure erases a person’s quirk. Brainwashing erases a person’s will. I can see how Brainwashing could come from Erasure.”

“That’s a pretty big leap,” Izuku argues. “Erasure is a strong quirk, so it stands to reason that some version of that would be passed on. But it also depends on what quirk his mother has to get Brainwashing from Erasure. I would sooner think that Erasure, combined with anything, would just create a weaker version of Erasure.”

“Quirk mutations are weird and don’t always make sense,” Todoroki says, which while true, still doesn’t bridge the gap between Aizawa-Sensei’s and Shinsou’s quirks. 

“Well, yes,” Izuku agrees. “But you can generally trace back where a quirk mutation comes from, or see how the leap could have been made.”

“And you can’t see how the leap could have been made?” Todoroki questions with a raised eyebrow. 

“Well, I guess--”

“Good, we agree. Next, we have to figure out who the mother is. Is she a civilian? Unlikely, considering Aizawa-Sensei’s… everything. Another hero, certainly. Another teacher? Possibly.”

Todoroki flips the board around, something Izuku hadn’t even noticed it could do. On this side of the board, is a collection of notes and printed-out hero ID pictures, all connected to a photo of Aizawa-Sensei. Izuku blinks, looking at the board in shock. There’s no way Todoroki is actually doing this. And if he is, there’s no way Izuku is helping. 

“Todoroki, I don’t have time for this,” Izuku says. Todoroki looks like he’s about to argue, but Izuku steamrolls over him. “Midnight-Sensei just assigned that research project, and now I have two weeks to learn what I can about Impressionist art. And I’m not even going to be able to make it to the library for a few days! At least! Not to mention Cementoss-Sensei’s homework, and Mic-Sensei’s analysis essay!”

“What the hell is Impressionist art?” Todoroki asks. “I got Renaissance art.”

“I don’t know! ” 

“Good luck with that,” Todoroki says, it’s only the fact that his sympathy seems genuine that keeps Izuku from tackling him. Still, Izuku vows to never give Todoroki another piece of information about Aizawa-Sensei or his family. 

Fuck, Izuku thinks when he makes it back to class after his lunch with Shinsou. I can’t believe Todoroki was right. 

Izuku spends the rest of the school day sulking. How had Todoroki figured it out before him? Granted, Todoroki was partially wrong. He’d been going from the angle that Shinsou is Aizawa-Sensei’s biological son. Shinsou had just confirmed that he was adopted. Still, it rankles at Izuku that he’d never even considered the possibility until it was staring him in the face. 

He can never know, Izuku decides. He settles into his seat with a firm nod, continuing his note-taking with more vigor. 

“I don’t know, Todoroki,” Izuku says, as blandly as he can make himself. If he’s too intense about it, Todoroki will just think that Izuku is trying to cover for Shinsou. Which he is, but Todoroki can’t know that. “It just doesn’t make sense to me.”

“Look at the evidence! ” Todoroki glares. 

“Most of your evidence is hypothetical,” Uraraka says, unwittingly helping Izuku. “Like, their quirks? Just because they both have mental quirks doesn’t mean they’re related. Erasure and Brainwashing are totally different.”

“And I hate to remind you, really I do,” Iida says, looking as put out as he sounds. “But my older brother and Aizawa-Sensei are friends. I more or less grew up around Aizawa-Sensei, even if I only saw him a few times a year. If he’s had a son for as long as I’ve been alive, I would know. Tensei is terrible at keeping secrets. My mother loves taking pictures. I would know.”

“And Aizawa-Sensei mentoring him doesn’t really prove anything,” Tsu points out. “I’m sure he would give any of us extra training if we sincerely asked for it. Their fighting styles are only similar because Sensei is actively teaching Shinsou his style of fighting. It’s not ingrained in Shinsou or anything. And if Sensei had been training him his whole life, biased entrance exam or not, Shinsou would have passed.”

“Right,” Izuku nods along with his friends. “There’s just too many holes. You need to expand your theories instead of just focusing on one. If we’re really stuck on him being a hero course student, have you considered he goes to another school? What about Shiketsu? Aizawa-Sensei and Ms. Joke have been friends since high school as well. It would be safer for him to attend there, as it’s not as notorious as U.A. And all the hero schools followed U.A.’s example of implementing a dorm system.”

“Oh yeah!” Uraraka jumps in. “That would be really smart of them! Shiketsu also has a really good analysis program, and Eri says her big brother is really smart.”

“I can’t believe you guys,” Todoroki shakes his head. “I really can’t.”

Izuku sits back and watches as the others start discussing the possibility of this new theory. Todoroki sulks for a while before reluctantly joining. 

Izuku mentally pats himself on the back for a job well done. Shinsou had better be appreciative for throwing Todoroki off his trail.