I have never seen any true logic to these type of outlandish coupling. One theroy some might have is that since Roxas is a part of Sora, which makes Roxas automatically "Makes him 爱情 her". Another theroy is the other way around with Kairi being Nanime. I can't think of any other real reason for THOSE people to think that way. Maybe it is the fact there is no real logic to it.
I think it's because Namini'e looks like her voice actor and Sora goes mad with power (later on) so the only people left in the group for couples is Kairi and Roxas
They are not. Sora and Kairi on the other hand yes because they have been there through the beginning. Roxas has been there only half way and is gone now anyway.