Here is what you know about Unknown Girl 1 at this point in the game.
She appears about as much as Unknown Boy 2 in the introduction FMV.
Seeing as how that wasn't a lot of time you can gather very little
about her. First off you need to be able to see that she is a "good
guy" (okay technically "good girl") judging by the way she looks.
Unkown Boy 1 seems to know her somehow allthough right now we can't
tell how.
Note: Don't read on unless you are extremely impatient or have already
played passed this part of the game. (SPOILERS ABOUND)
Kairi
The unknown girl is now known as Kairi. She is friends with Sora and
Riku. However she did not grow up on the island she came from another
unkown place. She doesn't remember anything of where she came from.
Sora, Riku, and Kairi are working on a raft to sail to another world.
Note: Don't read on unless you are extremely impatient or have already
played passed this part of the game. (SPOILERS ABOUND)