Why does kairi forget who Sora is

These are obviously spoilers: Kairi forgets who Sora is because when Sora's memories were taken apart, everyone who knew him or was linked to him in some way forgot who he was, just as he forgot them. Then gradually as Namine put Sora's memories back together people started to remember him. He was asleep the whole time, so I only assume he would forget the people he knew considering his memories were scattered.