The Five Keys, also known as the Keys of Magniverses, are the keystones of the four Inheritors of Destiny and the Keystone of Stephos.
When Stephos sealed the Magniverses in the Breaking of the Continuity, he bound them with his power but also with that of others, the Inheritors of Destiny. Every so many million or billion years all four "Pillars" would exist together.
Together, the Keys can form The Transcendent Light, an omnipotent power. They also have the ability to control time and space, because the bonds protecting them were created from the power of these people. Therefore, they can literally cause any timeline to merge or create another magniverse.
The Keys can call vast amounts of light from all over the omniverse, and are a great source of Cast Energy. The potential of this is limitless; the power than can be drawn from the keys is infinite.