I saw the power of being the only one who's covering a niche today. Usui Kuria aka Clear Rocket is a vtuber who watches rocket launches, and that's her niche. She's been posted about a couple of times on this thread before, she's been doing these rocket launch watchalongs for a while so she's probably established herself in the rocket enthusiast community as their go to vtuber for these things.
Today youtube recommended her to me a few hours ago and I clicked on her stream. She had around 10.5K viewers watching her, something that even most of Hololive would call a great number, and it probably wasn't even the peak number of that stream since it was 4 minutes after launch.
In this case it was the launch of a H3 rocket, a new made in Japan rocket that failed its launch (in a rocket ejection stage, not the launch itself) the last time they tried it a few months ago (this time it went fine). So it obviously helped that she was a Japanese streamer live reacting to a made by Japanese rocket launching from Japan. But still, getting 10K+ viewers as a niche indie vtuber is impressive at any time of the day.
EDIT: Looks like the max was 11.1K CCV, according to
https://www.vstats.jp/video/CfUcl2VMNgs