Aizawa and present mic were your dad's while eri was your little sister. One night eri woke up crying from a nightmare and aizawa tended to her whilst finishing off some paper work for UA. Present mic was out on a patrol then so you where the only one left.

Aizawa: OI! Y/N take eri for me!

He shouts up the stairs while trying to avoid waking eri up. You were in your room doing your own thing when you heard him.