There is a creature. His name is Zedar. He watches from a place, looking for openings into it. He takes the people who open holes into the place he watches from. He pulls them in.
Once, there were five holes.
I have a very old character creation concept that I often return to inspired by the thought of Planeswalkers in Magic: The Gathering--that they had limits. They have hard limits that they can't exceed, limits imposed by the multiverse they all have in common. Something fundamentally connects all of the worlds that they've ever walked. Not just their spark, not just the nature of the worlds their visit... something more fundamental.
Every player makes a character that contacts that fundamental thing. It is the realm from which all energy comes and returns. It can exceed their limits, expand their minds... and it can kill them.
Zedar is one such being. He looks for others with this power and takes them somewhere safe. It is a long and difficult process. And this is the first time he will have multiple wards to guide.
-Any passion can open someone's mind to The Void. An Artist, an Archmage, a Hedonist, a Prophet, a Lover, a Scientist.
-Any being can open its mind to The Void. A high school student in rural Iceland, a sentient fungi colony in a primordial soup, a space elephant, a sith lord, Shub-Niggurath, an artificial intelligence.
-Anyone from any reality or time can open their mind to The Void. Earth, Earthsea, Toril, Dominaria, Arrakus, Pern, Koprulu. Whatever. Whenever.
-No one can fight. If they had powers, they can't use them. If they had gear, it didn't come with them. Everyone is naked and barely able to hold it together, because where they are, the only thing that matters first is remembering who they are.
The story would revolve around every character learning about one another, learning who they are and how they connected to The Void. Zedar would be participant too, but is the only one who knows where this seminal experience will take everyone. It would be a cerebral and reflective work about a group of different persons coming into the first throes of godhood.