Hardest Ayu song to sing?

[CHE.R.RY]

^ I have a lot of trouble with that octave jump as well, so I know exactly what you're talking about.

I find myself struggling with:

1) Until that day... - she sings really fast and it's super hard to follow along ._.
2) still alone - the vocals are really screechy and really put a strain on me.
3) kanariya - you gotta go WAY up there. It's really difficult.
4) Connected - sometimes I can hit the notes, and other times...not so much xD