Sweet, I love a good brainstorming session.
For the VR host, an obvious solution to just throw out straight away is Discord, from Equestira. This would be straight up his alley. It's also a bit of a cop-out, so I'm inclined to keep that as sort of a last resort. Still, it could be framed as him needing to stir up a little trouble, and no one is going to mind, or even notice, if he works his magic in a universal branch so distantly removed from Equestria that no one else has ever been there.
Alternatively, and keeping with the Mediterranean mythos that lingers beneath the surface of the series, a Medusa-like figure could also be fun. Naturally gorgeous, mildly vain, and a tremendous flirt, it would be a good way to both encourage and discourage players from going down the path she intends for them. It would also be possible to use the Sirens here as hosts and attendants, if there was a desire to.
Dialogue is pretty straightforward; I could manage a couple clusters for each major NPC with relative ease. Just give me a structure to work off of, and I'll see what I can cook up.
The story is probably the hardest part, because I haven't played anything beyond the second Persona game. I'm pretty familiar with the other series, and the whole Lawful/Neutral/Chaotic branches and how they impact endgame, but other than that I'm sort of in the dark as to how we're looking to structure the whole thing. I know there was a flowchart to work off of posted at some point, it might be good to have that again.