everybody is doing the vibrato thing at the moment. I suppose it's meant to add some 'uniqueness' to the performance & also it's said to be lot easier & less-taxing on the voice to use vibrato than not to.
I personally still think Ayu's vibrato is tolerable eventho I'm hoping she'd tone it down a bit. I don't wanna mention names but I've heard a lot worse in a recent tour live of another big j-pop star which really dissapointed me
