"Earplugs"...

[Psychotic_X]

the earplugs are for the artist to be able to hear themselves and the music being played..
cause when sound travels there's a delay, so if you don't wear them sometimes, the artist is out of sync...

And cause Ayu's got that hearing problem as well as performing with a band and in an arena, the sound arrive at times much different to someone say sitting on the 3rd level of the last row compared to Ayu....
So the earplugs keep her in sync.. well keeps everyone in sync...

Kuu has smaller venues as well as backtracking, which she's used to...
And I think Kuu chose backtracking as a choice rather than to have a band...
but I think from now on she'll be with a band...