The System to be used is a Kit-Bashed form of Nobilis and In Nomine.
Other than that, the game is In Nomine for all intents and purposes. The Players are Angels in service to their chosen Arch Angels with the requisite hierarchy, perks and responsibilities.
The Celestials in Seattle have gone missing. Only the Cherub who is responsible for the Tether to Destiny remains. Yves has asked several Arch Angels if perhaps they could send one or two of their Servitors to investigate and assist in defending the tether if this is an assault launched by the forces of Hell.