It's absolutely not Ayu. The voice is clearly from a completely different set of vocal chords. I'm certain it is the "Jusme" person who is credited as the Vocoder voice, if for no other reason than the fact that there is only 1 vocoded voice in the track.

Coincidentally, Jusme is a name that has popped up elsewhere in J-Pop, writing the lyrics for "ALARM" for Amuro Namie, among several others (usually appearing alongside composer MONK).