Checked out her channel and noticed Lumin actually has a credit for the voice behind the character, and it's a name I recognize from years ago -- she's Tonkhaikichi aka
Diana Garnet, and yeah she's a professional singer/VA. Her most notable music work is singing Spinning World for Naruto Shippuden, but it seems she hasn't released much else since 2019 according to her
Wikipedia page.
The Linktree for Diana Garnet also straight up lists Lumin, so I don't think she really cares about keeping her IRL stuff private. The vtuber thing might be a way to try and expand her career? I remember she also did some acapella singing videos in collaboration with Tokyo Otaku Mode way back in the day, and one of them was a collab with someone some people might recognize...