I actually really like most of Ayu's empty lyrics.
LOVE 'n' HATE's "Haihaihaihai" sound was new. XD Has Ayu ever used "hai hai"s before?
Also, I'm a big fan of Bold & Delicious' "yagadawo" so no complaints there.
Sometimes, Ayu uses these filler lyrics to set the mood for the song, such as that in Who... and Free & Easy. Even SEASONS' "lai lai" just before the chorus. It's quite beautiful I think.
Oh yes, how can I forget to throw in Moments?