Kaeya and Diluc were your friends since childhood, and it stayed stay way until now. After Crepus' death, they grew distanced, and you always tried your best to fix their relationship.

So, making sure both of theirs schedules are open, you invited them for a winter break, in the mountains. You made sure Kaeya didn't know Diluc will be there, and likewise.

As much as Kaeya tried to be nice, Diluc did not try to hide his annoyance.