The Orator Baccus Sword is arguably one of the best one-handed swords attainable, including those Rune Weapons obtainable by use of Qualis Gems. It's high damage output, along with it's high Speed-n-Reach specs make this sword a deadly weapon.
To obtain this weapon you need to successfully defeat and capture the king of The Empire (Marius Imperator). Once this is done, engage on a conversation with him. If his kingdom has 6 or less castles+cities left, he will have a special option in which he trades his unique weapon for his freedom. This will remove the weapon from his inventory meaning the next time you'll meet him, he will use his secondary weapon.
This can only be done if the player is a Monarch.