This is a weapon that is more or less a 'key'. It's only a weapon in shape and design though no one but the Oracles have seen this in person. From what the Knight's do know is that the Blade of Adugran needed enough energy to be summoned forth (Probably enough energy to break into whatever was holding the weapon from being taken). The Knights also know that its a blade made of Arucite, a material that can absorb a massive amount of energy for a short period of time that can also in return be redirected from the stone. The blade is more likely a component to a more complicated puzzle.
Discovered in Book V. This information came from an interrogation of a captured Oracle Ally.