Three Keys

The World Tree holds as many worlds as it has leaves. Three keys are all it takes to replace the stablilty of the nine regions with an apocalyptic war, and the possibility of total destruction.

The Asgar and the Jotun hold one key apiece, and the third key changes hands from possessor to possessor. But when one of the soldiers of the Asgar deserts, that key is lost. With two keys on the loose, whomever can assemble all three can control existence.