Quote Originally Posted by OverPower
Man,I thought I read too much here.
At least,someone said that Kairi wasn't a princess by the sense of the word.She is a just "Princess" (read: "Princess") because she has connections with the keyholes and all that stuff. (Oh yeah,ans she doesn't has darkness is the heart)

Ansem wasn't a ruler,was he?Not even a King!

He was hust a researcher about the hearts,connections with the worlds,darkness,and all that stuff.........................................

End.
He was. Not a king, but he was the legitimate leader in charge of Hollow Bastion. He wanted to research the Darkness because he was intrigued by it, but of course, the original experiment/research was the dissection of the Heart, and its powers, which led to the research of the Darkness.

She is a Princess of Heart. Not a technical princess (although 5 out of the 7 are, and Alice could be considered one once she inherits a Kingdom in the sequel of In wonderland). All of these princesses have no darkness, supposedly, and are required to open the way to Kingdom Hearts.