Mumei. I share quite a few of her personality quirks, and of all the fantastic singing voices in Hololive, Mumei more than anyone else has the ability to make me just stop what I’m doing and listen.
On the JP side the one I follow most is Towa for similar reasons (holy shit her voice!), so you could imagine my excitement when Mumei sang Palette for the Connect the World concert.
Ghost brought me down this rabbit hole, Palette is my favorite holosong, and Mumei and Towa are my favorite singers, so those two performances had me over the moon.