Mha reacts!

The beginning

Class 1A was just doing what they do. Katsuki was beating up Izuku, Tenya was trying to break them up. Denki, Mina, Kirishima, and Sero were memeing, Fumikage was doing his 'Revelry in the dark' thing. And it wouldn't be a normal day if Monoma didn't insult them during lunch. Everything seemed normal.
Until a girl that seemed to be around 14 or 15 barged into the classroom.
"Hi! Sorry for barging in here, but I have some questions to ask you all. Can I?" She asked politely.
"Just make it quick, I'm in the middle of a lesson." All Might said.
"Thank you!" She then walked in front of the podium, blocking some of the stuff on the board.
"First question. Does anyone in here know what an AU is?" Momo then raises her hand.
"Yes, the girl with the black hair in the back! Could you also tell me your name? I never got the chance to learn your names." Momo them stood up.
"Momo Yaoyourozu. And if I remember correctly, it stands for alternative universes."
"Thank you Momo. And she's correct! Now, would anyone like to see some after your classes are over?" She responded. Tenya than raised his hand.
"Blue hair, in the back."
"Tenya Iida, and may I ask how this works?"
"Tenya, that is a very good question. So, the universe has parallels, like mirrors. Some very gifted people, such as myself, can travel not only through other universes, but other worlds as well! Anything else?"
"Do they have memes?" Kaminari asked.
"Yes. Yes, they do. And what's your name?"
"Denki Kaminari."
"Thank you, so does everyone agree to this? Everyone is coming, but those that don't wish to participate won't be forced to, and will be in a separate room to do whatever they please. If no one agrees, I'll just leave you all alone to do whatever you guys do."
"So, now with that out of the way, raise your hand if you want to come!" She added. Izuku immediately raised his hand wanting to learn more about her quirk. Denki, Mina, Sero, and Kirishima followed after for the memes. Koda, Sato, Mineta, and Aoyama followed shortly after just because, and eventually most of the class had their hand up.
"All Might?"
"Sure." He shrugged.
"Yay! See you all after your classes!" She then proceeded out the door, and class continued. At some point we heard a lot of noise coming from class 1B, but it eventually silenced.
After about an hour, class ended. Once the bell rang, the girl from earlier walked into the class room.
"Hi again! Just a little reminder, you all aren't the only ones there, so be respectful to everyone, even if there is some bad blood between you two. And no fighting, I don't want to use reinforcements. Cool?"
"Cool." Denki, Mina, Sero, and Kirishima responded.
"And please do this quickly, I don't do well with portals." She then opened a wonky portal and it looked like she had a hard time keeping it open.
"What are you guys waiting for?! Go in!"
"It's a bit too small for some of us." Shoji said. The portal was about the size of Mineta, so it would be pretty hard to fit through.
"Actually, I have a better idea!" She closed the portal, then reached into her messenger bag, and took out what looked like a glorified bouncy ball.
"How the f—- is that supposed to help us!" Katsuki yelled. She ignored him and tapped the gem that was in the orb; ball? Or whatever it was called. It then opened a portal that was bigger and more stable than the last one. She poked her head through but immediately closed the portal.
"Sorry! Wrong world. This doesn't always want to cooperate." Then she tried it a couple more times.
"Found it!" She directed us into the portal. Everyone walked in, and you wouldn't believe who we saw. There we about 60 other people there! It looked like we were in a theater!
"Tenya!" Iida's brother was waving from his wheelchair. {rest in peace Tensei, edit; his career}
"Tensei!" He ran to his brother, and then sit in the seat next to him. The girl then closed the portal and walked up onto the stage and took a microphone out of her bag. And tapped on it, which got everyone's attention. She then talked into it.

"Hello everybody! I'm glad no one decided not to participate! Please take a seat. Don't actually take one though. Heroes sit under the heroes section, villains under villains. If you don't apply to either of those, just sit where ever! Now remember to respect everyone here and no fighting! I don't want to resort to unnecessary precautions that are theoretically violent! Sure, out there you guys may be enemies, but in here you guys are all friends! Or at the very least, acquaintances. I'll give you all some time to talk and move your seats and stuff, but if you're going to start a fight, please stay where you are. That includes asking someone to move, there's plenty of space so that won't be needed. Thank you all for listening, and enjoy!"