Since the beginning of Genshin Impact, player’s been talking alot about Katheryne: Adventurer’s Guild receptionist.
She’s been known as someone who give traveler a lot of information and work related to Adventurer Guild. What’s so strange about her is sometimes she said something about “error” and then “rebooting“, suggesting that she is robot, android, or some kind.
She also have some kind of keyhole behind her neck.
Katheryne also have multiple presence in Teyvat, we’ve met her in Mondstadt, Liyue, and Inazuma. Most likely we will also met her in the other regions. She casually talk about this but never give traveler and paimon clear information about her multiple presence.
From Lan dialogue, we know that Adventurer’s Guild headquarters can be found in Snezhnaya. If you want to confirm this, you can find Lan near Katheryne table in Liyue.
With information above, it won’t be so weird to take conclusion that Fatui is controlling Adventurer Guild and using Katheryne for information gathering in all regions of teyvat.
And now, with recent trailer from Hoyoverse: Teyvat Chapter Interlude Teaser: A Winter Night’s Lazzo, all fatui harbingers show up and one of them seems related with our current theory: Sandrone The Marionette.
As described by Tartaglia , Sandrone always engaged in her research on Automatons. And in the trailer she’s carried by big automaton. towering her in height.
From this information, we can theorize that Katheryne is android, machines, robot, or puppet controlled by Sandrone to gather information or monitor certain individual. And that’s mean she’s been monitoring traveler since we arrive in Mondstadt.
I’ve found reddit thread discussing about this. You can find it here, posted by dream996.