There is Earth, our familiar world, and then there is the Black World, a parallel dimension that very few are aware of. For centuries, a pact between the two worlds has been observed to maintain peace, but terms must be renegotiated to continue the relative harmony. Taki of the human world and Makie of the Black World, two agents of the elite organization known as the Black Guards, defenders of the balance between the two worlds, are charged with insuring the success of the treaty against all threats.