Good day readers, this is the author speaking. I am somewhat experienced when it comes to writing stories, but this is just a fun little side thing I'll do when I have time. It'll take place in the My Hero Academia Universe, but will house extreme changes to help suit the storyline I'll be making. As such, the changes will be the following: Taking place after the War Arc and all characters involved at full power, including Izuku Midoriya having full control of his quirk. Please be aware I am not too knowledgeable on the power scale in MHA, or the characters, but I am learning about them actively. If things seem off with them, consider it part of the AU. I will also have a LOT of my own personally made characters that are part of my own universe. They will be crucial characters to the story, and fair warning, I do plan for character deaths. Be advised, this story will have themes of warfare, tiny amounts of romance between adult characters, and everything that happens in warfare typically. Viewer Discretion is Advised.
That being said… Welcome to "The Clash of Universes"
Chapter 1: The Calm Before the Storm

"Sensei! Why did some Heroes from before not believe in the fundamental principle of saving innocents?" Asked Mina, while a disgruntled Lida remained nearby in the hospital room, that reeked of blood and hospital grade cleaning chemicals. "Probably due to some Heroes only in it for the money." Was Lida's reply, which irritated Aizawa. "Problem child, some heroes are true heroes, and others are heroes for the pay. Like us, they have family to look out for as well. This may simply be a job they need to survive. After all, Hero society as a whole is being heavily looked at now that the dust is settling." Lida and Mina could only nod at that. It made sense, in a twisted way. Todoroki walked in at the end of the conversation bearing a flummoxed look.

"Guys. Remember how Izuku lost his quirk after defeating All For One?" He asked his peers and teacher, who nodded. "What about him, Problem Child?" Todoroki had to take a seat in a nearby chair, his knees weak while he thought about how to explain things. "From what the doctor said… Izuku's quirk came back. At full strength. They're… both horrified and amazed." The squeal that came from Mina almost made Aizawa cringe as she was right beside him and had just squealed in his ear. "That's amazing! Deku will be the greatest hero of all time!" She said happily while jumping for joy. Apparently no one had told her that she was still in her uniform and accidentally levitated Todoroki, who just floated upside down glaring at Mina… Which was quickly wiped from his face as he fell to the ground due to Mina releasing her quirk. Luckily he was in a hospital because he broke his nose from the fall. "Problem Child, control your quirk!" Aizawa corrected harshly, instantly quieting Mina's celebration.
"Sorry Sensei! Sorry Todoroki!" Todoroki could only grumble in silence as he opened the door holding his nose as he sought out a doctor to treat his broken nose. Eventually Bakugo walked into the room as Mina finally calmed down enough to not murder Aizawa's right ear from her squealing. "Alright extras, quit squealing I can hear you in the adjacent room! Besides, did any of you hear what the government said?" Aizawa just stared Bakugo down at that statement. "Problem Child, we all heard the government's statement about the war." Bakugo scoffed at him. "Not that! Some nerd from a science institute detected some kind of signal from deep space! It's got everyone in high gear. Apparently this was a once in a lifetime discovery!" Everyone went silent at that statement. A signal? From deep space? That wasn't possible! No one went into outer space anymore! Not even satellites! How could there be a signal coming in from deep space!?

"It's true." A familiar voice spoke up in the room, with everyone looking up to see All Might in his deflated form with Izuku Midoriya behind him in his Vigilante uniform. "They detected a signal from deep space. They're still trying to decrypt it as we speak, but rough guesses suggest a… blueprint. We don't know what for yet, let alone if it actually is a blueprint. One thing is for certain, it's not following our known methods of communication. It seems to travel on energy waves itself." Aizawa scoffed as All Might spoke, with Izuku still writing notes meticulously. "Travel on energy waves itself? Whatever you're smoking All Might, I need some." Drawing a horrified gasp from Ida. "Sensei! You cannot do drugs as a hero! It also violates UA Policy-" Ida was promptly silenced by Bakugo making an explosion in his fist silencing him. "Extra, even I don't believe it myself, but if it's got the nerds in an uproar, what makes you think they don't know more than we do now? We've only got second hand information, and the nerds in the government are way more excited than they ever were before. There's credibility here. Ever heard the phrase 'Where there's smoke, there's a fire'?" Everyone went silent for a few minutes processing what was just said.
"Did… did Bakugo just say something intelligent for once?" Was all Izuku could say quietly, speaking for the room of silent people. "HAH!? You want to die extra!?" Was the usual quip from Bakugo which everyone promptly ignored. "Problem Children, this is a unique situation. There's the possibility that this is just a distraction from what happened to get everyone's minds off what happened not too long ago. There's also the possibility that this is a signal from… well this will sound insane, but an advanced alien civilization. Maybe it's just solar radiation too, we don't know. Right now, all we have are theories and no real facts. We can't make sudden judgments or rash decisions. We shall wait for more information." Left unsaid was the discussion on if it was an advanced civilization… were they friendly or hostile?

"I don't know about you guys, but I am not worrying about this 'signal'. Not until we have more information." Said Midnight who came walking into the room. "Good afternoon Midnight. I assume you heard the same thing we were talking about?" Aizawa asked as Izuku finished jotting down his notes about the signal and his own personal theories regarding the entire incident. "That would be correct. Though from what I heard in the grapevine, the signal is confirmed to be blueprints. Extraordinarily alien in design, and runs on principles that I didn't even know were a thing. Some kind of… starship. We don't know. It's extremely alien to us. It also appeared to have a symbol of a world with three swords embedded in it. It's unlike anything we've ever seen, but I personally worry about what we're inviting here trying to take that signal. If someone is truly sending it… wouldn't they know someone picked up the phone?" Midnight said, drawing a lot of worried looks from everyone. "That… is a scary thought. I still think it's solar radiation though." Ida said, drawing worried chuckles from everyone. After all… the possibility of someone being on the other end and… picking up the phone was horrifying. Especially when you didn't know if they were friendly or not. If they're advanced enough to be sending signals the way this one was… they most likely had some form of advanced space flight.

"I doubt it'll come to that. If it's a hostile alien species, then we just blow them to smithereens!" Shouted Bakugo, drawing a few confused glances from nearby hospital staff who proceeded to move back to what they were originally working on. "Way to draw attention to us, Baku-bro." Kirishima said from the doorway. This of course turned Bakugo onto him. "Shut up Shitty-hair!" Little did the heroes of 1-A know… something was coming.

"Sir, we're detecting some kind of… energy wave. Once again, it's riding waves of pure energy. Only… this seems to be an audio file? It's highly advanced, even by their standards. Once they captured enough of it, they ran translation software for several weeks. Eventually it was translated, but no one could predict what they were about to hear.
"All hands, battle stations. Let's pound these bastards into hell and back." Said an unknown voice, transmitting the audio through space. "Sir, hostiles are opening a gate to flee." Said another voice. "Chase them down. Show no mercy."
As one, the scientists were horrified. Something had fled… something, and was being pursued. There was other life out there… and it seemed even more hostile than humanity ever was. That alone… made them question just what was out there, let alone what a 'gate' was. As such, they quickly brought the information to the government, who had to decide what to do next.