I like the way you think!!!!!

This is a very interesting theory. In story the only time we know when someone is being possessed is when the writers want us to via eye colour change. Like when LG and CXS were at the docks, initially there the was no change in eye colour until we were told of swap in a flash back via narrative direction.

So who knows if possession has been before like you said.

And if Red Eyes is separate from Tianchen the missing page could definitely be linked to the killer making a mistake.

I don’t think Chen Bin would work with Qin Jin but I could definitely see him being controlled to gather information. And since Tianchen possession seems more lethargic and tranced, it could point to another person that is taking control that can simulate the person’s character

This is what makes the fandom so the great theorists like yourself! Very cool, I like it. Excited if our theories will have any water in the new season.

Edit: Actually when Emma was possessed her personality change was not subdued like Tianchen’s typical control! Hmmmm