When Dracula's Castle becomes aware of the awakening of its master, it sends its Blood to take control of many of Dracula's minions, and uses them to try and hide away his power in areas of the Castle he will not be able to reach without his full strength. Among the first to become corrupted are the Jailers and Dungeon Minions, which steal the Void Sword from its resting place in Bernhard's Wing and hide it in the Toy Maker's Guest House. The Keeper is the Jailer who actually carries the Sword, and even though the weapon is a metaphor for Gabriel Belmont's emotions, just holding it has granted him relatively weak Void-based abilities from it. Alucard must defeat him to retrieve his father's weapon.
After a fierce fight, Alucard retrieves the sword and decapitates the Keeper using both the Crissaegrim (charged with Igneas magic) and the Void Sword, before returning the weapon to its pedestal in Bernhard's Wing. Notably, this wouldn't be the Castle's only attempt to prevent Dracula from retrieving the weapon; as he approached the Sword himself, the Blood possessed a pile of broken statues and attacked him in the form of the Stone Golem.
Serving the orders that the echo of the castle gives them, the Dungeon Jailers quickly hid the Void Sword to keep Dracula from finding it on his return. The leader, more corpulent and better armored than the rest, carries the weapon clumsily, followed by a group of henchmen with little interest in self-preservation. Despite not understanding how its magical properties work, the Keeper of the Void Sword seems to be affected by the energy that envelops it, making him able to project it at will. The enormous beast's fascination when contemplating the cold blade of the Void Sword makes it clear that no creature will be able to take it away from him, except over his dead body.