The Six Meridian Divine Swords is one of the Duan Royal Family's top arts along with Duan Family Swordplay and the Yi Yang Finger.
The most powerful of the Duan Royal Family arts, the Six Meridian Divine Swords requires a profound and abundant internal energy level to successfully wield it. Other than the Creator of the Six Meridian Divine Swords, Duan Si Ping, Duan Yu from the Jin Yong novel Demi-Gods and Semi-Devils is the only other person who has ever mastered all Six Swords. Even then, this was considerable amount of time after Demi-Gods and Semi-Devils story ended.
Six Meridian Divine Sword is in fact a set of sword techniques that replaces a real sword with internal energies to utilize. In the novel, there were numerous instances when people using Swords and Daos (single-edged swords) had their weapon struck by Six Meridian Divine Sword, it was implied that user felt like their weapons just clashed with a sharp metallic weapon such as a sword but with inhuman force closer to the likes of Desert Eagle, a modern firearm. Moreover, Six Meridian Divine Sword channels Internal Energies through 6 different Meridians, thus allowing the user to perform rapid fire like a machine gun. It's only limitations is the strain on the user's meridians and their internal energy reserves.
Duan Si Ping, the Creator never had problems.
Duan Yu absorbed the Internal Energies of a dozen top martial artists, giving him vast amount of internal energies.