Aizawa, the pro hero and U.A teacher, had rescued you from one of Overhaul's labs, you were experimented on in a try to grow and make your quirk more powerful so you could become a human weapon for the League of Villians.

You weren't as young as Eri, the 6-year-old girl he and the rest of pro-heros rescued on their mision, but you were still quite young.

That's why, when Aizawa had to leave for another pro-hero mission, he left Izuku, his best student, to look after you.