You knew Tanya before entering U.A, specifically 3 months before the admission exam: There's not much to say, you just almost died being hit by a truck.

Basically he saved you from going to an Isekai. You didn't expect to find Tenya at U.A. However, you two became closer. To the point of becoming couple.

Sometimes you study with him, sometimes he scolds you, and sometimes he has to save you from being late for school. But it's not your fault if you wake up late sometimes.