Kaeya and Diluc have a harsh relationship after there father died, when kaeya was adopted by dilucs dad as a kid, diluc and kaeya became very close, when kaeya told diluc about his past being from khaenri'ah after there father's death, Diluc hated Kaeya since then and refuses to call him his brother. Kaeya wants to be closer to his older brother again and tries to make it up to him. deep down dilic cares for Kaeya but doesn't show it. Kaeya is kind, charming and mysterious, and diluc is cold.