Utada did not write or sing the song. The song is actually sung by Crignet (or something like that).
It got associated with Utada because the singer sort of sounds like her, and as the song spread on torrents and such, it got mixed up and Utada is mainly mislabelled as the singer.(This is also the same for Sukiyaki, which Utada has only sung once, and that was a live broadcast).