I will now perform my civil duty as for what is expected of me and say that it was probably
not Kairi's Memory that Sora saw.
Aside from the obvious "Kairi never acted like that" which is easily explained with Naminé wrapping her up in her image, we have two very obvious contradictions to that claim -
1)
Sora said:
I can't nor will I ever want to stop stressing this enough. Naminé from the beginning was
separate from Kairi. For obvious reasons hers were the Memories that were pushed aside the most, but that doesn't change the fact that for the longest time, Sora didn't remember Tidus, Wakka or Selphie, or even
Riku for that matter! It's not like he really remembered anything from Destiny Islands, so he had no way of knowing Kairi was missing. All he truly knew and cared for was Naminé, whose importance was shown in Memories that
had nothing to do with Kairi, being the drawing issues and the Promise on the night of the meteor shower.
Kairi being there or not being there was all but redundant, as was Tidus, Selphie, Wakka and Riku's presences in the long run.
2) KH1.
Last time I checked, the one that was paired up with Kairi by TSW was
Riku. All but praising him as the undefeated, almighty god of the Islands, TSW constantly repeated how lucky Kairi was for having Riku, and how Riku could always take care of Kairi if ever she needed anything.
Sora was shrugged off as the lesser man which is probably why Selphie let herself make half a move at him by saying she could share a Paopu with someone better than Tidus and Wakka.
Couples based in KH1, being Sora's true Memories:
Selphie/Sora, Riku/Kairi.
Couples based in CoM:
Sora/Naminé, and Riku possibly running off - to the girl that had no importance in the Memory Sora was seeing - Kairi.
So no. I'd hardly say Naminé was sitting in Kairi's place during the Destiny Islands Memory Floor.
To top it all, that was the part in the game where Naminé seems to be actively trying to drive Sora away. I mean, the good luck charm changing back? Who was it that changed it in the first place, huh? And you'd think that if
Kairi was really that important to Sora someone's importance to Sora would've truly kept Naminé's powers at bay, that none of CoM would've ever happened. Yet alas, it happened, and Sora forgot everything which was truly important to him regardless of its importance, so much that he even went against Donald and Goofy for Naminé's sake. I think it kind of shows that we can't use anything from those scenes to truly judge Kairi's importance to Sora.
Naminé changed the good luck charm back to try and make Sora think of someone other than herself.
Naminé came into the Memory World and told Sora not to listen to the other her. Now why would she say that had it been a Kairi underneath and not really a Naminé, hm? It was a struggle of wills, between the Naminé Sora wanted to be with and that wanted to be with him back, and the Naminé that wanted what was best for Sora, even at the cost of her being with him.
When Sora refused to listen, she resorted to the only thing left up her sleeve - and that was to convince Sora he cared more about someone else than he did about her.
An effort that ultimately failed, seeing how he was willing to give up on his Memories regardless of realizing he had forgotten, but in her defense let it be said she did try.
Bottom line though -
One Naminé was the Naminé that existed in Sora's fake Memories, and the other was the real Naminé that came to try and stop Sora - when it was already all but too late.
