I Pledge the Following as your DM:
I will not have each of you create your characters and then immediately take everything away from then. This campaign does not start out with imprisonment, amnesia, stolen items and equipment, or kidnapping. These seem to be heavily repeated themes in modules, adventure paths, and homebrew games of late.
The premise of the campaign will however hinge on the characters' acceptance of an invitation to participate in the events to come.
For reference, much of the concept and theme of this campaign is influenced by the Eternal Champion cycle by Micheal Moorcock and he has several instances in his books where difference aspects of the Champion join together for a common purpose. IE: The Four Who Are One and the Sailors on the Seas of Fate. Essentially the PCs in this campaign are erstwhile aspects of the Eternal Champion or potentially so for different planes of the Multiverse. There are fifteen planes of Man in the Multiverse that we can draw from.
The use of the number Eight in this instance is also an homage to the very first D&D campaign ever noted run by Gary Gygax called The Citadel of Eight and later the Circle of Eight. Their goal was to maintain balance between Good and Evil, Law and Chaos. Sound familiar?
It is from this campaign we got Mordenkainen, Bigby, Robilar, Riggby, Yrag, Tenser, Serten, Otis and later Bucknard, Drawmij, Leomund, Nystul, Otto, and Rary.