Four girls from different points in time end up trapped in a book called The Universe of the Four Gods. They are the Priestesses of the four countries the universe contains. You know the story of Fushigi Yugi... a girl and her 7 protectors summon a god who grants 3 wishes. But what if the story was different?
Takiko and Suzuno both ended up in the book but their stories never took place. After Miaka summoned Suzaku, things changed a bit and all 4 girls are in the book at once! Miaka and Yui are trapped in the book and cannot go home. Tamahome has lost all memory of loving Miaka. The other Seishi (both Suzaku and Seiryu) do not remember their relationship either.
The story can play out from here. It's like a fresh start for the girls and their seishi, so feel free to control them however you like. The story can be tweaked so that Seishi who should have died can still be alive instead or can continue as ghosts.
How many seishi are involved is unimportant to the story, so the girls don't need to go around hunting out seishi. However, the seishi can feel the presence of their Miko in this world and are drawn to it. It wouldn't hurt for any Genbu or Byakko players to move towards Konan or start out there.
I have done extensive work in laying out a plotline that doesn't require all 28 seishi present and explains the discrepenices this places between the manga and this rpg.
Hopefully there's some interest (there's pretty much EVERY character available) so check out the community. The info section is huge and details lots of questions you might have (though feel free to ask here if you're interested).