Utada Hikaru wrote and performed yet another Japanese hit, but this time was able to wow the audience of a very successful video game. As Rahul mentioned in the OST, the theme song is designed to flow with the Destati theme. Having musically brought Kingdom Hearts to life together with Yoko Shimomura, Utada is certainly a force to be looked upon with appreciation.
Her single comes complete with a karaoke version, so for those of you that way inclined, you can sing away. Look out for her, she's very talented.
The western release of the OST does not include the Japanese versions of the theme song, so it is in fact another addition to the original release.