aside from my usual ragbros + mond trio? I think Lisa and Kaeya. I like to think Lisa is a good few years older than Kaeya and not really a big sister, but she's someone he entrusted his love life and more intimate worries because I mean come on. Around the time he was hitting his late teen years/adulthood, his dad keeled over, Diluc left, and he can only entrust so much to Adelinde. So I like to think he went to a more neutral person who he knew was known for taking care of those younger than her, and developed his own relationship with her outside of work that is Just them