Theorycrafting time!
So we're talking a ton about the Shikigami and his Onmyouji possibly being evil right? I think that's a total red herring and now I can understand why they brought Childe in.
Ok so I think it's already a pretty safe guess by now that Childe is on a Fatui mission and is investigating this Domain. What I think he's here for is that the Fatui are under the assumption that Harunosuke is actually evil. So with an evil and powerful onmyouji he'd make a pretty powerful Harbinger right? I think Childe's here to recruit him.
BUT on the other hand what if Harunosuke is good? And what if Harunosuke is powerful enough to detect malevolence? The Fatui have been in Inazuma for a while. They were responsible for Ei enacting the Vision Hunt and Sakoku Decrees after all. And we know how hateful they are because you can't not be hateful and use a Delusion. (Poor Teppei) So what if Harunosuke lured Childe in?
What if - ok I have to use my version of the story to make this make more sense - after deposing Ei and leaving Sara to pick up the pieces of the broken Tenryou Commission and Kokomi's secession of Watatsumi this left Inazuma in a very weakened state. Just like what Childe said. So hidden somewhere deep in the land was this powerful onmyouji who was always watching over Inazuma in case they needed him one day. That day is now so he sees that Childe is going to be big trouble since the man's likely the strongest of the Fatui or at least as strong as Jester. He lures Childe in with the monsters figuring out that he just loves to fight. And this Domain is an endless fight after all.
This is why he isn't getting out each time we are. Harunosuke is letting us leave but he intends to trap Childe inside. Childe for now doesn't find a problem with this because he doesn't realize he's trapped and he doesn't realize Harunosuke is playing him. But in the next part all will be revealed. And that final battle that was mentioned will be against Childe. I mean we already had a normal boss to fight right? Makes sense the last challenge could be a weekly. (But sorry we're not going to get a freebie farm out of the deal haha)
Of course we're not really trapping him here forever. It's just a way to leave him out of the story for now. I mean he wasn't really in the story anyway after Liyue. It's just a nice excuse not to have him show up for a while. Also it'll be a way to demonstrate how powerful he actually is. We'll learn from Harunosuke that Childe is too strong to contain for long but he'll do his best. We might even get another event out of the deal if we have to come back to this Domain to fight Childe again as he starts breaking loose. Man I could totally envision a horror-themed version of this event with Childe haunting us as we travel through. Like out of nowhere he'll do his dash attack and then disappear. It'll do tons of damage and we just have to watch out for it.
What do you think of this theory?

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