The Book of Armaments

From the introduction:

In [each] round of play, each player takes on one of three roles: the Wielder, the Weapon, and the World. The Wielder player takes the role of the protagonist in this part of the story, they're the one who has possession of the weapon. The Weapon player is responsible for making sure the option of using the weapon to solve problems is ever-present in the mind of the wielder (the weapon may not be a sentient entity itself, but it is significant and attention grabbing for the wielder). The World player is responsible for describing the world around the Wielder, playing all the other characters in the world, and introducing adversity into the situation.