@pedronekoi: The whole song has the same audio channel, and during 3:30 she lip-syncs to the wrong lyric (the second chorus instead), all pre recorded vocals. That's the scene that SunshineSlayer was talking about.

Ayu is not trained to do sing and dancing at the same time, and it seems that she's like "I will perform the song live, even if only half song, but I'm not sing with a backtrack helping me".

This is actually how she performed up until 2003. She used a backing track before she had PECO and Princess.

Every time an Ayu concert is mentioned there are always the experts that come out and explain how everything is edited or lip synced or a backing track was used or alternate vocals were used etc.

theme of a-nation '03 was probably the weirdest use of back track she's had. Like... why? IIRC it was pretty early on in the concert and she was standing in one place for the whole song. It wasn't like when she shows up with a head mic and you know basically all of the song is being mimed.

Did it have some hard high notes? Don't really recall this song.
Well, she didn't move during Carols and Momentum in CDL 13-14 either, but lip-synced them anyway, but these songs are quite difficult to sing....

Is Over hard song? She lip-synced it at PCDL

It sure is a hard song, I almost never try singing it at karaoke. :D

PCDL also had a very long setlist, way longer than she was used at the time, some tracks probably were lip-synched just to preserve her.

She was also on hella painkillers, lol

You can also lip-synch parts of the songs, use a loud backtrack or loud back up singers that makes going off-key less noticiable and there are choreographies that aloud the singer to sing somewhat well. ^^

Beyoncé, for example, usually has choreographies that keeps her standing still when she must sing.