In Darker than Black there are Contractors. They have a "contract" which means they can cast one particular spell, after which they have to complete their "cont

In Darker than Black there are Contractors. They have a "contract" which means they can cast one particular spell, after which they have to complete their "contract payment" before they can cast again. That's often a simple but annoying task like smoking a cigarette or writing a poem. The spell and payment are different for each one. Nobody got to choose. http://darkerthanblack.wikia.com/wiki/Obeisance http://darkerthanblack.wikia.com/wiki/Obeisance