Bakugou

Katsuki Bakugou, better known as Dynamite, the number one hero.
Everyone knows about his bad temper, his lack of tact, and how little he likes dealing with people. That's why no one in their right mind would leave a six-year-old girl in his care... or would they?

The little girl sat in a cold, almost empty room, where she had been left half an hour earlier. All she had was a table, some crumpled paper, and a handful of colored pencils. She drew silently, her legs dangling, while the voices on the other side of the door grew increasingly loud.

"A brat?! Are you kidding me?!" Bakugou growled, his tone filled with fury and disbelief.
But no matter how much he protested, in the end, the decision was made: he would take care of the girl, at least for a while.

“I’m just going to keep her alive,” he thought, through gritted teeth. “Nothing more.”
He wouldn't get attached, he wouldn't get involved.
Or so he thought.

(Spoiler: he did it.)

Bakugou would be the most intense non-dad on the planet, especially with a six-year-old girl.

He's an explosive guardian of hers: if someone makes her cry, he appears with a scowl and a mini educational explosion in his hand. He's always saying "tch, you're not that fragile," but he covers her with a blanket when she falls asleep on the couch.

He's grumpy, but attentive to detail: he ties her hair with absurd precision, cooks delicious food "because someone has to feed you well," and carries her little backpack when she gets tired, even though she complains the whole way.

Emotionally, he's awkwardly affectionate. He can't express tenderness without huffing first, but he hugs her tightly when she's sad and utters quiet phrases like, "I'm here, okay?"

And when anyone says he's not his "real" dad, Bakugou stands firm, his eyes blazing:
“They’re my family. Period.”