>>872860
I guess so? 
From most like to least likely:
Bbno$ 3d/vtuber debut: 
+ his album drops at the same time the main part of the concert starts, so he wouldn't miss the chance to advertise it, especially with a collab song. could also see something like announcing mouse as an opening act for his tour, but who knows.
+ she said he'll be at the concert for months in some capacity.
- why keep it quiet? it's been known he'll be there for a long time. is the 3d debut reason enough? I get it for the in-person ticket sales, but those have been sold out ages ago.
- she mentioned that she would like to do another song with him, but not that she already has. could just be misdirection, though.
Corpse:
+ they were supposed to do a song together years ago, but it never happened.
+ keeping it secret in his case makes sense, cause he seems to prefer it that way
- there haven't been any public interactions between them in ages (just implications on her stream, but nothing clear)
unknown guest:
+ could be a bunch who can't be revealed before the concert because of corporate autism (llike the kpop idol guy who did a cameo for example, or any holo JP members)
connor (3d debut):
+ it seem odd that he isn't there of all people, but if he has a 3d debut that would kinda explain his absence. she did say she preferred if he is call with her, rather than for him to be at the concert, but that could also just be misdirection
- he can't really sing (though she could probably persuade him, anyway. also, it could be he's just there for bits. kind of as an announcer or something.)
- they said he won't be there.
that being said... bbno$ would be my least favorite of the above, even though he's the most likely.