Listen, no artist is or should be invincible to criticism. Let's be real here, this performance was not good vocally. It's okay to have a critical opinion of Ayu at times. Or any artist.
Having a negative opinion of Ayu's performance does not make you a bad fan or a traitor or "hater" as many people online like to say. Defending her poor performance does not make you a better fan either. Actually, these people are part of the problem.
We love Ayu and want to see her succeed and give a powerful performance just like we know she is capable of. It upsets us when she fails to deliver, whether it is her fault or not. I think her inconsistent vocals are largely beyond her control.
It is because fans love her that they feel disappointed and criticize her. Sure perhaps some people just are rude or being jerks, but based on the posts I would say many fans just want Ayu to do well! I know me personally, I want Ayu do deliver an awesome performance so she can finally give a big middle finger to all of the nasty people who heartlessly bash her. It would be sweet revenge.