This one is the result of chatting with heyhamlet, and realizing the AU I had snowballed with him, was in fact entirely fitting for Whumptober 2019 day one "Shaky Hands".
When they were little, before their quirks had come in even, Katsuki and Deku had made up a language. Rather- they had made up code words and phrases.
Back when they had been convinced they would be heroes together, and nothing and no one would stop them.
As little children, that language usually referred to things like school, and their mothers, and a father, and various other things and places and people that they had interacted with.
And Katsuki would never admit that, even when they had their falling out, when Katsuki had thought "Deku couldn't be a hero quirkless", he had never let himself forget that series of codes. That when he was bored, or had a moment to himself, he would still think them over, whisper them to himself, and make sure they were second nature to his mind.
That somewhere, deep down, he had never doubted for a second that Deku wouldn't claw his way into heroics somehow.
So Katsuki remembered, and never let himself forget what they had whispered to each other, out in the forest where they used to play.
And then Deku had gotten a quirk, had trained and trained and fought for his place in UA, and their relationship improved.
Teachers that cared, and wouldn't put up with his shit, as well as anger management and counselling and certainly helped that along, after their fight in Ground Beta.
After the various disasters and villain attacks that had befallen their class over the years, Bakugou had finally taken a moment- right near the start of their second year-to sit Deku down and see if he remembered the codes.
Of fucking course the nerd did.
He should have known better.
Still- he had made Izuku promise to use them, if he ever needed to. Said he would make sure Izuku got the help he needed, if he did.
Class 3-A had a well established series of...tasks, that they went through if they were, at any point, going to miss school or be late.
It had become a requirement, after all the villain plans, kidnappings, attacks, and plots they had gotten themselves caught up in.
Which was why, when Deku was late, and no one knew where he was, or what the hold up was, there was a sense of panic, tightly controlled, amongst the classroom.
Deku was a nerd and he liked to show up early to classes. This had held true throughout his entire school career, though UA in particular held a high place of honor for him.
Katsuki knew it was because Deku had friends here, and not just because he was eager to learn how to save people and be a hero. Granted this wasn't so much a class as it was the meeting place for the class after a weekend at home with their parents or family.
But the point still stood- even here, seeing his friends again after a weekend with Auntie Inko...the nerd would have been early.
So when the class tricked in, as their time limit to be back on campus for Aizawa to do a final headcount, started cutting it close and Deku's desk remained empty…
They were all agitated, and scanning the area, looking for that curly green hair.
Katsuki knew Izuku was supposed to be here. He'd texted the nerd last night. He'd said he was packed and ready to head back to the dorms.
Aizawa-sensei was standing in front of his desk, leaning against it, instead of curled up in his sleeping bag like he usually would have been until the last minute. He was switching his gaze from the door to the clock, and then scanning over his students.
Katsuki fidgeted. The scent of burning sugar was growing stronger as he fought not to set off sparks in his agitation-not worry, agitation- and stared at the door like Deku would just appear.
It's five minutes past the cut-off arrival time back to UA, and Aizawa has already alerted the Principal, when Katsuki almost jumps out of his desk and falls into a combat stance on instinct.
The tense hushed conversations the class had been having cut off.
Katsuki's phone is ringing.
Katsuki's phone never rings. Especially during UA hours- any one who would call him now-a-days goes to UA with him, and his mother knows that even in emergencies, she has to contact UA directly to talk to him.
All parents signed a document saying they would follow that procedure when they went through the multitudes of paperwork to be part of the Hero Course, resigned and agreed to at every new year. Their class- as targets for villains- is especially held to this standard.
So Katsuki's phone rings, and the class falls dead silent as he reaches into his bag, face pale, but determined.
He knows the ringtone. It's from an old All Might anime that he and Deku used to watch together, and Katsuki had assigned it to the nerd forever ago.
When he flips his phone around "Fucking Nerd" stares back at him from the caller ID, and Katsuki steels himself as he accepts the call.
He immediately presses the phone onto speaker, and the class is dead silent as Aizawa steps closer to his desk and they all stare.
Katsuki doesn't even get a chance to open his mouth and ask Deku 'where the hell are you, you fucking nerd' the way he wants too.
Instead he hears Deku call, in a falsefalsefalse happy tone "Hi, Onii-chan!"
And Katsuki's heart stops.
But Izuku keeps talking "I know there's not a lot of time left before school starts, but if you could tell Sensei I'm not gonna make it in today? And let mom know I'll be late too, I broke her vase, and messed up my assignment for class, so I need to replace that, and fix the other at the library, before I can make it home."
Katsuki's brain automatically translates the codes spilling out of Izuku's mouth, even as his face pales, and his hands start shaking.
"I'm in a large amount of danger. I don't have much time, they're hurting me, and I can't leave. Bones are broken, the case I was one went back, you're going to need info on it."
Katsuki is going to throw up. The only thing holding him on his feet-when did he actually get up- is the strong grip Aizawa-sensei has on his shoulder.
Izuku's phone is state of the art. All of 3-A's phones are. Hatsume had 'tinkered' with them too, so the entire time the conversation happens, as naturally slowly as Izuku can make it sound, the entire class can hear some of what happens in the background.
There's screaming, crying, the sound of someone being slapped. There's an angry voice snapping commands.
Izuku's voice doesn't waver.
Not even when, closer, and crystal clear to the class, they hear a male voice snarl "Hurry the fuck up Deku." The boy's hero name is sneered, thrown down like a gauntlet.
There's a moment of silence broken by the clear- too clear and close to be anyone but Deku himself, even with Hatsume's changes to the phone- sound of a bone snapping.
"It's time to hang up, little hero. We wouldn't want any...accidents to happen to anyone would we?" the same voice growls.
Katsuki's legs start shaking, just like his hands, and he sways where he stands again at the sound.
At how steady Izuku's voice still sounds, despite the fact that he just had his bones broken.
"Anyway, I gotta go Aniue, love you, goodnight."
"The danger has escalated to deadly, and I make not make it, I love you."
Katsuki doesn't even feel his phone slip out of his hands. Doesn't feel the way he tries to pull out Aizawa-sensei's hold.
He didn't even get to say anything back.
He didn't get to say anything back.
That was his BROTHER and he didn't get to say anything back to him-
Aizawa-sensei's hands are either one of his shoulders, the class still dead silent despite the heavy pulsing aura of rage they are all giving off, despite the look in their eyes that says they are only still and silent because they are waiting for a direction to move.
Katsuki's hand tremble as he claps over Aizawa's hold on him and demands "Let Go."
"Bakugou, I need you to tell me what happened."
Aizawa-sensei is pale. He's an Underground, he knows code when he hears it, he's taught the class some. But his eyes burn like pits of hellfire and lava, a conviction just as strong as the one in Katsuki's chest.
So Katsuki answers. "Izuku has been taken somewhere, he's hurt bad, the situation just turned deadly, and we're on the clock. It has something to do with the case he was working on with the remains of Nighteye's Agency, and if I can find his stash of notes- his 'library', I can limit where we have to look."
He shakes his way free of Aizawa and starts running.
He crashes his way towards the dorm, towards Izuku's room. The Nerd was always brining work home- if he could find where he'd fucking hid it this time, he could help.
Like fuck he was going to leave his friend- his family damn it- in the hands of villains.
(He can hear his teacher and classmates falling into step with him.)