A long time ago, you (a villain), fought a group of villains alongside Izuku (a hero), as your goals happened to be the same in that moment—and Izuku presumes you also wanted to save your own skin. Now, when he's become a pro hero and is officially patrolling the streets on his own, he can't help but to be nervous at your sudden reappeareance and the fact you're following him so shamelessly.