Third person PoV:
Class 1A we're having one of their usual squabbles. Then Aizawa stood up in his yellow cocoon of sleeping bag and announced tiredly to the class, "There's a new student be nice or whatever, I don't care. I'm going back to sleep. Don't kill each other". Then rolled to his normal sleeping spot and fell asleep.

The door opened and a student walked in.

"DEKU?!?" Katsuki yelled "WHY ARE YOU SO LATE?!? AND WHY DO YOU LOOK LIKE A GIRL?! AND WHY ARE YOU TALLER?!? AND CHUBBIER?!?"

"Umm Kacchan...", Izuku murmured surprised, "that's not me"
The student who walked in glared daggers at Katsuki.

"He's right Kacchan" They said, putting emphasis on the "Kacchan" part, "I am Mika Midoriya, Deku's older twin sister. I'm late because I was keeping it a secret from my baby bro, I look like a girl because I am a girl. I've always been taller than lil Deku and I'm not chubby, I'm fluffy". With her last statement she put her hands on her hips and flicked her vibrant green hair.

"You go girl!!" Mina yelled from her seat, Mika smiled at her. The rest of the class was in a shocked silence. Except Izu who was red from embarrassment.

"HA! EVEN YOUR OWN SISTER CALLS YOU DEKU, DEKU! YOU'RE SO WORTHLESS!!" Katsuki yelled at Izu.
Mika glared at Katsuki again. If looks could kill, Bakugo would have died several times over. Mika spoke clearly and darkly, "Listen Katsuki, I've been ill most of my life, but I've seen the damage you've caused. Ever since you started bullying Deku I have been studying you, planning my attack on you. You have such a big head but such a small brain. You know... I could tell all your secrets right here, right now. But I'm a nice person, so I'm not going to... I'll tell one and only one. But not before doing THIS." With that her eyes glowed green and so did Bakugo. When the light faded, instead of Katsuki, there was a small, fluffy and angry Pomeranian. The Pomeranian imminently started borfing very loudly.
Class 1A erupted into loud whispers and shouts. Kirishima scooped up the Pomeranian and stroked it to try and calm it down.
"SHUT UP!" A dragon-like girl yelled "THIS GIRL OBVIOUSLY HAS SOME SECRETS ABOUT BAKUHOE! LISTEN TO HER!" Mika grinned and nodded to her as the rest of 1A looked at her expectantly.

"Okay, two things. I know I said I'd only tell one of Bakuhoe's secret's but I've got one of Izu's secrets as well and it has something very much to do with Katsuki." Mika announced to the class " Katsuki's secret is... he was best friends with my baby brother" the entire class gasps "I know it sounds like a lie but it really isn't, do not talk to Katsuki about it". The class sighed in annoyance. "Well I guess you could tease him a bit about being friends with Izu, but don't blame me when he blows you up." Mika smirked. The class erupted in giggles and murmurings.

"SHUT UP!" Yelled the dragon girl.

"Thanks, urm... what your name?" Mika asked politely.

"Tsuno . Tsuno Rezu. Never call me Tsuno, but you can call me Rey." The girl grinned at Mika.

"Cool, thanks Rey." Mika grinned back.

"How come you never let me call you Rey, Rezu??" A blonde boy with a black lightning bolt in his hair questioned whiningly.

"Because Kaminari, you're not my best friend... and you're annoying" Tsuno replied.
Kaminari pouted and Mika blushed a little at the title of best friend.

"Thanks Rey, anyway onto Izu's secret." Mizu said and the class cheered. "So, I'm feeling nice... or technically mean to Bakuhoe. Did you know that if Izu calls Katsuki by his full name instead of Kacchan. Katsuki will hide, terrified".
The class exploded into laughter.

"ONTO IZU'S SECRET!" Mika yelled over the noise and the class quieted down.

"You know how Izu calls Katsuki, Kacchan? Well does anyone know what Kacchan means??" Everyone shook their heads. "Kacchan is a name for men who sleeps with different man every night." Mika finished.
The class was silent.

"MIKA HOW DARE YOU TEACH YOUNG, INNOCENT DEKU WORDS LIKE THAT" Iida announced, annoyed, doing his usual karate motions.

"I didn't teach him" Mika shrugged.

"She's right" Izuku murmured.
Class 1A gasped extremely loudly. And bombarded him with questions. It got so loud that Aizawa woke up and sent them to there next class. Rezu and Mika talked all through their classes.

At lunch Izuku walked up to his sister. "Hey Mika," he called to her, "as it's your first day, do you want to sit with my friends and I?". Mika smiled at him kindly,
"As much as I'd love to sit with you, I'm going to sit with Rey if that's ok with you?" She replied kindly.
"It's fine go on with Rezu" Izu said with his classic smile on.

COMMENT CONSTRUCTIVE CRITICISM!!! AND STUFF YOU LIKE!!! AND STUFF YOU DON'T LIKE!!
Sincerely,
Me