My Hero Academia/Boku no Hero Academia - Becoming Eri’s Parental Guardian would include... (Headcanon)
Teaching Eri both in and outside of U.A.
Eri learning that she is loved and cared for.
Her starting to call you “Mother/Father.”
Being appointed as the parental guardian by the faculty of U.A.
Becoming VERY protective over Eri.
Teach her the pros and cons of her quirk.
Having Izuku and Mirio over at the house often to see how she is doing.
Leaving her in the care of Aizawa in case of being called in to do hero work.
If Aizawa’s not there, then Toshinori.
Eri’s quirk being in handy in case anything breaks.
Threatening ANY boys and girls if you seem so much as stare at Eri.
Being the most violent teacher at U.A.
You being the first person Eri shows any emotion to before the Sports Festival.
Telling her how proud you are.
Telling her how much you love her.
Making sure she prioritizes her studies over anything else.
Explaining how the professional hero business works.
Making her very first hero outfit.