Potentially interested! I have a few questions, though:

Since you mentioned Jojo, is the implication meant to be that our Summoned Demon is sort of "one of a kind" like a Stand or a Persona? Or will we negotiate with other Demons to build a multi-person party, and if so does the Player control their subordinates as well as their own character?

Does anything keep the players from leaving the city, like a barrier of some kind? Is this sudden invasion of Demons something that only happens in the given location, or is the whole world suddenly plunged into an apocalyptic scenario of some kind? If it's the former, will this play out similarly to the Devil Survivor games?