In Kingdom Hearts, this comment is found at the end of Ansem's Report 11:
"If the princesses and the Keyblade are connected, they should resonate. I have chosen a girl. I don't know if she holds the princesses' powers, but I will find out. She may lead me to the key bearer. I shall set her free and observe."
In Birth by Sleep, after Aqua and Mickey save Kairi from the Unversed, Aqua places a charm on Kairi's necklace (which she has worn for the entire series) and states this about said charm:
"I just cast a magic spell on you. One day when you're in trouble, the light within you will lead you to the light of another. Someone to keep you safe."
By the content of the Ansem's Report, Kingdom Hearts suggests that Kairi ended up on Destiny Islands because her heart resonated with the Keyblade. However, if the dialogue in Birth by Sleep retcons the account in Kingdom Hearts, then Kairi was a regular victim of the attack on Radiant Garden, and the charm of her necklace drew her to Sora. If both accounts are valid, then Xehanort's Heartless sent Kairi out suspecting she was a Princess of Heart and expecting her to be drawn to the Keyblade naturally, but Aqua's charm hijacked the experiment and led Kairi to Sora regardless. DoubleCross (talk) 17:04, December 12, 2013 (UTC)