hmmm, i watched that performance again. i think she has problems with those really high notes (ex: "you-u... calling you") she sounds extremely out of breath. as for yuna ito, seems she has no problem as when she sings "kawaru"... in "Precious". here's the performance:
http://www.youtube.com/watch?v=_UOBRv04CRg
she has one of most beautiful voices of Japanese singers. as for stage presence, it all goes to Ayumi Hamasaki.