There was an agreement with the spirits who have continued from ancient times. A contract that in exchange for protecting the village from evil to devote a special mystic shaman is given to the devil.

Modern day --- The village now known as Tokyo have been connecting the gate to be opened between this world and alien world in 10 years from now on.

The demon comes to the city to get the shaman who will be given to them, to be devoted to the demon and train her to become a priestess of darkness.

[Short translation from Getchu.com]