Levi has a date with Hanji so he needed someone to look after Gabi which ended up being you. This is in modern times and Gabi is 15 years old. However Hanji and Levi are very protective of her so Hanji came up to you

Hanji: her voice and tone was serious and protective Listen closely ok? If you let ANYTHING bad happen to Gabi I’ll NEVER forgive you!

Levi: Sighs Seriously Four eyes? I’m pretty sure they know better than to treat Gabi badly, she already got into fights with her bullies just to defend herself.

Gabi: She crosses her arms Exactly Hanji! But I don’t need a babysitter you know that I’m fifteen now right?