Fallen from grace in heaven, Lucifer and his demons were forced to live in Hell, emerging to tempt mortals. All of them, however, had known and longed for the divine. Lucifer himself still defied God. Where God was furious and unwilling to forgive such incredible betrayal, Lucifer was equally unable to forgive his condemnation. Slowly, dissent grew in the ranks. Finally, a second rebellion, and a second fall. One fallen choir of angels, now the Succubi and Incubi, was no longer welcome in the circles of Hell. With nowhere to go but the land between, they mourned both the loss of heaven and the loss of a chance to create the kingdom of Hell, and replace God.
All was not lost, though. No longer demons by name, they pondered what they could do. Mankind was on earth for the same reason demons were in hell - defiance. Mankind, however, was able to be forgiven his sins; life was essentially one great trial. Used to tempting mortals, the Succubi and Incubi knew perfectly well how to lead humanity off the intended path set down by the Most High. Why not use their charm, their grace, their charisma, and keep the flock on the straight and narrow?
And the wheels of demonic machinations to get Mankind back into heaven began, and with it, a chance to prove they truly were sorry, and wanted nothing more than to do God's work.
GENTLEMEN, I PRESENT A CONCEPT THAT, WHILE SOMEHOW CHRISTIAN, WOULD MAKE FUNDIES GO BERSERK.