Kyouko Kasodani is a Ten Desires character. She's a part of the Myouren Temple.
We were on the situation "regardless of spellcard thievery" purely because we're the player character. If we were controlling someone else I'm sure NPC Nue would have been amenable to sit in her bar and keep business open, if not take advantage of her knowledge of gem value to charge exorbitant prices. Having spellcards stolen gives Nue plot motivation to go out and kick some ass regardless of her player status.
(Of course, given how meta this explanation is, this does mean I have no intention of making Nue consider my theory until and unless she is given good in-game reason to do so.)
EDIT: I forgot to mention this earlier, but I am not yet convinced that Metal Gear Nue should be our primary attempt at getting information out of Eientei. I can think of several circumstances where it would the most appropriate action, but as long as all we were directly told by the streetear was that a rabbit claiming to be our friend visited, we can simply travel to Eientei, apologize for being unavailable, as inquire as to what the visiting rabbit desired of us. The question of what happened to our spellcards can (and should) be brought up after we hear the rabbit's explanation, and it should be brought up as a curiosity question rather than an accusation. After the number of times assumptions bit Iku in the ass last game, I am leery of the potential ramifications from using less well-seeming approaches to the rabbit situation, such as trying to sneak in uninvited or busting in (no pun intended) and flinging accusations of theft.
If we act innocent and get suspiciously denied information or entry, then that would be the time to use our disguise.
