Four year old Izuku Midoriya pulled a small girl behind him towards kindergarten.
This girl was his new little sister Kurai. She had just been adopted into the Midoriya family, at the pleading of a teen hero named Hawks, who claimed he couldn't protect her.
So far all she had done was cry. She had beautiful wings, just like her brother, but her legs had been shattered by a villain, which is what prompted her adoption.
After some rehab, she could manage to stand and walk on her own, but the doctors had recommended she just fly everywhere.
In the midst of this, Deku had discovered he did not have a quirk. It was hard watching Kurai struggle with her own quirk, when he would never have one.
Her quirk, living in her wings, was called clairsentience. So she knew her new brother was suffering.
Kurai insisted that Deku shouldn't give up his dream, that he could still be a hero. So now he was going to prove he was a hero. By being her hero.
"Cmon Kurai." Deku urged. "it's ok…it's just school…I'll protect you."
Kurai hid behind him "But what if they make fun of me coz of my legs, Zu?"
Deku smiled at the nickname, then gave her a determined look. "I won't let anybody hurt you Kuri."
His new little sister nuzzled against him. "Okaaaaay."
The two Midoriya siblings went inside.
"Zuku!" Reiko Bakugo ran up and hugged Deku right away. Surprisingly, his bully's twin sister was Deku's best friend. She let go, staring at Kurai. "Who's this?"
"This is my sister!" Deku cried excitedly. "Midoriya Kurai. She starts today so be nice to her everyone!"
Kurai bowed shyly. "Nice to meet you all." Her wings floofed at the attention.
Katsuki Bakugo noticed the newcomer, and came over to meet her. "Since when do you have a sister Deku?" He snarled, looking at the winged girl.
Reiko interrupted her grumpy sibling. "I'm Bakugo reiko! And that hot head over there is my brother Katsuki."
"Kat and Kit!" Kurai beamed, proud of herself.
Deku was embarrassed. "I told you not to do that!"
"B-but it's kewt Zu!" Kurai protested.
"W-Why am I Kit?!" Reiko asked.
"Cuz your a fox. A kitsune." Kurai pointed at her ears and tail.
"Whoa…no one ever figures that out…"
"If I'm Kat then your Birdie!" Bakugo pointed at her.
Kurai liked that a lot. She flitted around. "Birdie birdie birdie! I'm BIRDIE!"
"Aw kacchan Lookit what you did!" Deku groaned.
"Tch." Katsuki said, trying to hide his smile.
Kurai landed on his desk. "Thanks Kat!"
Bakugo stared at her. Why was he letting her get away with this crap? His quirk crackled in his fingers and he aimed it at her—
Kurai stuck her face right in his hands, and he jerked back instinctively. That was close! He almost blew her face off!
"What the hell are you doing?! I almost made fried chicken!"
Kurai grinned. "But your quirk is so coooool Kat."
"It is?" Bakugo's eyes widened at the complement, then grinned proudly. "Damn right it is!"
Deku glared at Bakugo, scooping up his sister. "Kacchan leave my sister alone! She's with me!"
He carried her back to his seat, Bakugo's glare following him.
Kurai pouted "Ano…zu…" She looked at Bakugo, remembering how much Deku was suffering from not having a quirk, feeling his insecurities, and she nuzzled her big brother. "Okaaaay."
Meanwhile, Bakugo glared over at them. A rivalry was born, as Bakugo stared at the cute little birdie that Deku wouldn't let him have.