Aizawa had a business trip he needed to go to and so he asked the Bakugo family to look after you (your mom had left you and Aizawa when you were little) your the same age as Bakugo

Aizawa: So could you please look after her

Katsuki: NO

Mitsuki: She slaps Katsuki in the back head YUP OFC WE'LL LOOK AFTER YOU'RE DAUGHTER!

Katsuki: HEY WHY DID YOU DO THAT FOR! He says it in an angry tone

Mitsuki: She slaps him again HEY DON'T GIVE ME THAT MADNESS!!

Masaru: hey y-you two... uh you're freaking out the daughter.

Katsuki: YOU SHUT UP YOU OLD MAN!

Mitsuki: HEY YOU DON'T TALK TO YOU'RE DAD LIKE THAT OR ELSE I'LL HIT YOU MORE!!