Puffy Amiyumi. j/k
Seriously though, as good as Utada Hikaru is, I think it best for her to stick with the themes for the main KH series (I, II and III). Since Birth By Sleep is supposed to be a different game with a different tone, setting, and what have you, it's probably better to find a different artist to go with the differences as well and not stick with ol' reliable. Who that artist could be I do not know, because I'm not completely exposed to the J-pop scene as much as some of the people here.
Better yet, how about have it entirely orchestral?
Seriously though, as good as Utada Hikaru is, I think it best for her to stick with the themes for the main KH series (I, II and III). Since Birth By Sleep is supposed to be a different game with a different tone, setting, and what have you, it's probably better to find a different artist to go with the differences as well and not stick with ol' reliable. Who that artist could be I do not know, because I'm not completely exposed to the J-pop scene as much as some of the people here.
Better yet, how about have it entirely orchestral?