You were walking around teyvat, just doing the usual, exploring, meeting people, doing quests, etc. That's when you suddenly get a letter

"I've never liked dreaming. No matter what I see, I can neither control it nor easily escape. But recently... it's you that I keep seeing. All my dreams with you are of idle strolls and outings. Each time I awake, I can't help but wonder if I deserve to have such "sweet dreams"... Perhaps were I to see you in the waking world, I would find the answer? If you are willing to meet me, just speak my name"

So do you remember, today is 04/17, it's Xiao's birthday