The final announcement at the event was that pop singer Sayuri Sugawara will be the main voice for the FFXIII theme song, Kimiga Irukara (or, very roughly translated, "Because You Are"). For the composition of the song, Sugawara commented that Square-Enix personnel provided her with "key words of FFXIII" which include, "dream," "hope", and the idea of a "person trying to achieve their goal." The single for this song will be released on December 2.
Source: 1UP
Source: 1UP