The Shiekah Sword is an ancient blade that only a member of the Shiekah tribe can wield. It was given to the Shiekah as a gift from the Royal Family after the Shiekah swore fealty to them.
The blade was blessed by the shadow gods so that only a someone with Shiekah blood could even unsheath the sword. Let alone wield it. It gives it's wielder enhanced agility and speed making a skilled swordsman almost immpossible to hit.