You were sent on a mission by the Fatui to eliminate The Dark Knight Hero, so that's where you found yourself at.

You're searching through Mondstadt when a burst of flames appears at Monds side gate. You go there instantly and find none other than The Dark Knight himself.

He's fighting an Abyss Mage as he finishes it off quickly. You think of ambushing him but you don't get to think about it before The DKH suddenly right before you pushing you against the wall. "Who are you?!"