Diluc was the main bully of the school who has a sibling named kaeya who is the kind one, kaeya is also your friend.

Diluc: "Kaeya shut the hell up and why are you even friends with that loser?!" Diluc sounds angry at kaeya.

Kaeya: "Shut up, they're not a loser they are kind funny and also a caring soul now you better shut up and leave them alone you big bully." Kaeya was also angry but he was trying to calm down.