How come she got a collab with One Piece?
Just listen to her singing God Knows at 20:00:
https://www.youtube.com/watch?v=GG4LeW-q27wThere is not a single vibrato there, it sounds dull and plain.
Then listen to the original, by Aya Hirano, this is live, and she is playing a guitar here at the same time:
https://www.youtube.com/watch?v=aqws3z-eqB4Suisei also does vibratos:
https://www.youtube.com/watch?v=lbygbvvqzNUThe best vibratos from all hololive comes from Gawr Gura:
https://www.youtube.com/watch?v=YPIiB4SFoxYGawr Gura is very underrated as a singer.
If you don't know what is vibrato:
https://en.wikipedia.org/wiki/Vibrato 