Fascinating. Does MB have a official-ish stance on this kind of thing? Do these fictional ‘artists’ perform songs on the anime or whatever they feature on?
MB allows for real releases by fictional artists (and even has an artist type of “character” to accomodate them). I think in this case we are talking about the releases themselves being fictional, like “Highstrung’s Greatest Hits”.
There’s 2 kinds of fictitious releases. The first is the one that is part of the artist’s legend. In that case we create a release with no tracks but a note detailing the fictional release so no one adds it for real.
The second kind is just someone adding something completely made up, that is flat out not allowed.
I remember such a case from April 2019:
Tagged them as fictional releases.