So can someone explain what the proper tagging is in situations like this? I understood that you need to tag "what you see" and since it's not confirmed in this picture that the hand is Lui she shouldn't be tagged. Are there exceptions for when there's a companion picture from different perspectives like with these pictures?

Deear said:

So can someone explain what the proper tagging is in situations like this? I understood that you need to tag "what you see" and since it's not confirmed in this picture that the hand is Lui she shouldn't be tagged. Are there exceptions for when there's a companion picture from different perspectives like with these pictures?

I think "tag what you see" would just take precedent here. As you've said, you can't really tell whose hand this is in the image without external knowledge (the other perspectives). It may as well just be a random hand. In my opinion, each image and its tags should stand up on their own, rather than relying on context provided by other images.
Imagine you're searching the database for pictures of takane_lui and this comes up. It wouldn't be particularly helpful.
Somebody searching for Takane Lui would of course find the version that actually features her in it, which these alternate perspectives are parented to, so they would still be able to find these alternative perspectives if they were interested.

I did actually remove the sakamata_chloe tag from the other version of this image a while ago for this exact reason. I was looking for pictures of Sakamata Chloe, that image popped up, I figured "that doesn't make much sense" and 'fixed' it.
I'll do the same for this perspective for now, just for the sake of consistency.
Hopefully that isn't the wrong decision but anyone is free to undo it if they believe it is.