You have a cat quirk, meaning you can turn into a cat. While in cat form you tend to roam around at night just because you like it.

One day while wandering around at night in your cat form you hurt your ankle and had to limp home. While on your way home with your injured ankle Aizawa found you and being the cat lover he is he took you home. He didn’t know that you’re actually a person with an act quirk though.

When he finally got you home he set you down on his coffee table and gently bandaged your hurt ankle.