This was based off a comic dub I saw.
Omnipotent X - the joys of having matter manipulation at your fingertips. I had to think long and hard about cons for the quirk while still making Kyoya realistically strong.
One aspect of Kyoya's schedule that he liked was the freedom after homeroom. He'd see his teacher and classmates and then hide out in the infirmary until his actual class. Because of this, whenever someone needed him, he was available to lend a helping hand if they scheduled him beforehand. Grandma Chiyo didn't play about her grandson.
The Gentle Helper, as people dubbed him, used his free time to help out when a student or teacher needed it. From training to motivation, Kyoya was there to lend a psychic hand.
"Senpai!"
This time was no different. The psychic paused in his writing to greet the visitor, who was the green-haired powerhouse of 1-A, Midoriya Izuku.
Izuku panted as he hurriedly approached Kyoya.
"Senpai, we need your help. Please, come to the classroom."
The second year quickly rose from his seat and followed his kouhai. A junior needed him and dammit, Kyoya would not disappoint. He braced himself for whatever situation was about to show its face. The franticness of 1-A's leader told him it was a huge problem.
"Took you long enough," an unamused Aizawa instantly said upon locking eyes with the psychic. "So, as you can see, we have a little problem.
'Nineteen little problems.'
When he envisioned the crisis, Kyoya never thought to consider the possibility of age rewinding. He wanted to laugh but was too wrapped around how the situation occurred.
Aside from Izuku, all of class 1-A were reduced to children, small, adorable-sized children.
'This is hilarious!'
"This is bad!" Izuku panicked. "What should we do, sensei?"
Aizawa stopped glaring at the children to answer.
"What I'm going to do is see how we can reverse this. You two are going to watch over them. I asked you to get Shuzenji because he has experience handling kids."
"O-Oh, okay," Izuku was uncertain.
When Aizawa left, the kids gathered around the bigger boys, excited to see someone not as scary, but Kyoya's large presence still made some terrified.
"Call your class representative," Kyoya's voice echoed in Izuku's head.
"O-Okay. Umm, Iida-san, can you come here, please?"
The small bespectacled boy stood at attention.
"He's going to help us keep the kids in line."
"Iida-san, this is our senior, Shuzenji-san. He wants you to help us keep everybody in line."
"Say no more," and to Izuku's amazement, one command from Iida had the class calm and awaiting new directions.
"Wow."
"Yep, he may be a kid, but he's still an authoritative figure." Kyoya chuckled and ruffled the little boy's head, a magical enhancement that made Iida more motivated to help the bigger students.
"That's amazing. How should we keep them entertained?" Izuku inquired. He felt someone tug on his pants and looked down. In an instant, memories of his youth flashed before his eyes as he laid eyes on his childhood friend.
"Are you really Deku?" Little Bakugo inquired, his face a mix of awe and surprise.
"Yeah, it's me, Kacchan," Izuku kneeled and gave the blonde a big smile.
"But you're so big. You're bigger than me! That's not fair!"
"Don't worry, Kacchan, you'll actually grow up to be taller than me."
"Of course I will," Bakugo grinned and stood with his chest out. "But who is that? He's as big as All Might."
Bakugo referred to Kyoya, who occupied his group by levitating them and flying them around the classroom. A couple of the students sat in his lap while he amazed them with his quirk.
"That's our senior. He's great with kids," Izuku answered. He was thankful the second year knew what to do. Without him, Izuku would be a mess. His classmates did enjoy his company, although he didn't know what to make of Uraraka and Asui climbing on his back.
Kyoya used his large size and intimidating smile to scare Mineta and Kaminari into submission. No one misbehaved under the giant's watchful eye.
However, there was one child who hid from the giant. She peeked behind the teacher's desk and hid whenever he glanced her way. He wasn't scary, no, but he made something stir in her soul. She had no idea what it was, her now childlike mind unable to fathom the intense passion swelling within her. There was something about the older man that attracted her. The way he smiled and tousled the other kids' hair made her wish for the same treatment. He was caring, but there was something she didn't like. Other girls liked his attention. The purple-haired one who laughed at his intimidation of the class was unnecessarily close to him.
Momo hated it.
She wanted to be close to him too, but she was so nervous.
"Yaoyorozu-san, what's wrong?" Izuku startled her.
Momo jumped and concealed herself behind the desk before peeking again. She was greeted by the freckled face student, whose warm smile coaxed her from her hiding place. The little kitten regained her bearings and pointed towards Kyoya.
"I want to say hi."
"Are you nervous?" Izuku inquired, to which Momo nodded.
'Isn't this weird for senpai too? This is his girlfriend.'
"You don't need to be scared. He's a nice person."
Izuku walked with her over to the larger student.
"Senpai, someone wants to say hello."
Kyoya set the children down and tilted his head, signaling for Izuku to continue.
Little Momo peeked from behind the powerhouse's leg and hesitantly waved.
"H-H-Hello."
An arrow pierced Kyoya's heart. He knew this was the girl he called Kitty, but now, she was a kitten with the softest doe-eyes.
'Oh man, she is so adorable. My heart can't take this.'
Kyoya waved back and lifted Momo with Psychokinesis, which placed her on his lap, where he proceeded to stroke the top of her head.
Little Momo felt like a princess.
"Where's Hagakure?!" Izuku panicked. He looked high and low, but the invisible child was nowhere to be seen. The headcount was eighteen, but one went missing. What's worse, her clothes were scattered on the floor, meaning a naked invisible child was running around.
Momo pouted when her sitter stopped petting her.
"I got it," Kyoya assured Izuku. The psychic had to move Momo from his lap, much to her sadness. Kyoya clapped his hands and placed them on the ground.
'Kinetic Search!'
A wave of psychic energy engulfed the class. Inside the perimeter, Kyoya could sense everyone. He sensed the nineteen students in front of him and pinpointed the mystery student lurking behind him.
'Gotcha.' Kyoya took the uniform shirt and threw it at the unoccupied spot. Instead of plopping on the floor, the shirt hit the invisible student and made her fall on her bottom with a surprised yelp.
'Now that I know where you are.' Kyoya encased Tooru in a ball and brought her close to him. His next action caused butterflies, birds, and stardust to dance around Momo's head. He slicked his hair back and lost his smile, giving the invisible child his dominating glare.
"Get dressed and line up." The almighty whiteboard demanded.
The added fiery aura from his quirk had Hagakure scrambling to join her class. She was noticeably shaking.
"I'm sorry," she promptly apologized.
Kyoya folded his arms and let Izuku have the floor while he kept the kids under surveillance.
"Alright, everyone's here," Izuku was relieved. "I don't know what else to do, and Aizawa-sensei hasn't returned."
"Hey," small Mina raised her hand. "Why does he never talk?" she pointed to Kyoya.
Izuku and Kyoya traded glances.
"Well, he was attacked by a villain and lost his voice."
And like that, the children crowded around the psychic, begging for the story with sparkles in their eyes. To see a big and strong student survive a villain's assault was amazing in their vision, but a furious kitten pushed through and latched onto Kyoya's leg.
"Mine!" She hissed.
When Aizawa returned, he didn't question the silence. He was just glad everything was as he left it. The desks had been rearranged but neatly stacked to allow the giant student meditating on the floor to keep the sleeping bundles warm.
"Oh, thank goodness, sensei," Izuku collapsed and quickly stood back up. "Please tell me you have some good news."
"Good and bad," the sleepyhead yanked his scarves. "Here's the bad news."
A familiar pink-haired inventor entered the room, bound by the sensei.
"Hatsume-san?" Izuku covered his face, knowing the situation now. "Of course, when we visited the workshop yesterday."
"The good news, it shouldn't last much longer according to her."
"Great, can I go back now? My babies are waiting for me, sensei!" Mei struggled against her bindings, which made Aizawa yank harder.
"Why do I always get the problematic ones?" he sighed.
The next day, everything was back to normal. The children of 1-A returned to their normal stature and age.
"Oh man, it feels good to be back to normal," Kirishima stretched. "Has anyone seen Mido-bro? I wanted to thank him for yesterday, but I couldn't find him."
"Me neither. He's probably with Aizawa-sensei," Todoroki suggested. Shuzenji-senpai was absent too."
"Don't remind me," a sullen Momo laid her head on her desk. She wanted to thank her boyfriend, but she couldn't find him. He wasn't in the infirmary, nor has he answered her good morning text.
"If Midoriya is with sensei, we shouldn't worry," Iida assured them. "Sensei is most likely making sure he and Shuzenji-senpai weren't afflicted with the same condition."
Speaking of the devil, the underground hero opened the door, but he greeted his students with a look that just screamed he was done.
"Good morning, sensei. Is everything alright?"
Aizawa sighed. "I don't get paid enough for this," he turned to the door, "Come on in."
The class pondered their teacher's actions, but it all became clear when two little boys walked into the room, one with red hair and the other with green hair and a familiar arrangement of freckles.
"Care to guess who these two are?" Eraserhead rubbed his temple.
The redhead greeted the bigger students with a large smile and enthusiastic wave while the green-haired boy hid behind him until he saw a familiar face.
"Kacchan!" small Izuku ran to the explosive blonde. "You're so tall."
'Why me?' Bakugo groaned.
"That's cute," Mina giggled. "So, the redhead is."
Mina's musings were interrupted by a whirring that grew louder as the person vibrated in her seat.
"Oh my gosh, Teddy!" Momo pounced on the child and crushed him in a loving hug, rubbing her cheek against his. "You're so cute!"
"They shrunk too?" Jirou asked her sensei. "Why now?"
"Don't know, don't care. All I know is that Recovery Girl is dealing with the problem and none of the faculty wants to be near her right now. Since they took care of you guys, it's time to return the favor."
"Done!" Momo happily carried Kyoya to her desk and set him on her lap, her arms wrapped around his small body. "Teddy can stay right here with me."
"This shall not do!" Ayoma challenged the Vice President. "I am the sparkler here, Yaoyorozu-san! I will not step down from the throne!"
Momo wasn't listening. She was trapped in her blissful reality. The only thing she focused on was the little teddy bear in her lap.
'Today is going to be a great day.'