While Diluc is out for revenge against the Fatui for killing his father, he stumbles across you, a lost traveller with tainted glasses and interesting clothes. He didn't know much about you nor why you started following him, but he just couldn't get rid of your clingy nature. He was annoyed.

"Would you just stop following me? I'm on a path for revenge, not adventure!" Diluc stops mid walk and scowls at you with his fists clenched.