The Azure Knight, previously known as "Nightmare", the former wielder of Soul Edge who brought the world to its knees... In truth, he was first a knight named Siegfried. After killing his father by accident, Siegfried fell into a deep denial, which eventually twisted into a desire for revenge against his father's imaginary killer.
To enact his revenge, he needed power, which lead him to Soul Edge.
Turned into the sword's puppet, he became Nightmare, until losing in battle to Kilik. When the sword was shattered, Siegfried found himself awoken from the strange spell he had been under. Though freed from Soul Edge's grasp, he now had to face the fact that it was he who killed his father.
On the ground to his side lay the shattered remnants of Soul Edge...
Unable to cope with the weight of his crimes, Siegfried tried to abandon what was left of Soul Edge. However, the evil sword was so closely tied to his fate that it would not relinquish him from its grasp so easily. His cruel reign as Nightmare was not forgotten by any means, and, one after another, warriors began to appear before him, intent on taking their revenge.
Wandering aimlessly, Siegfried ended up crossing swords with a woman who declared that she must destroy Soul Edge. Though she claimed to be able to purify souls, the deep-rooted evil gnawing away at Siegfried was too strong to be cleansed. Nevertheless, their meeting would prove the necessary impetus for Siegfried to vow to face to his sins and atone for them.
Soul Edge could not be scratched, let alone broken by a normal weapon. To ensure the sword would never again fall into the hands of another, Siegfried decided it would need to be sealed away somewhere in total isolation. However, such a place was not easily found. Meanwhile, every time he struck down another challenger who sought revenge against Nightmare, Siegfried feared that he was in danger of slipping back under the sword's control.
Not all who stood in Siegfried's way were hell-bent on revenge. Some warped souls appeared drawn to the evil of Soul Edge. Though it wasn't Siegfried's goal to do away with these twisted individuals, neither were they the types with whom he could reason.
The evil in Soul Edge was growing stronger with each passing minute. One day, Siegfried heard an ethereal voice in his head speaking directly to him. Responding to Siegfried's desperation to save his own sanity, the spirit sword, Soul Calibur, was calling out to him. But from the sounds of things, the blade was also in need of help itself...
The moment Siegfried gripped the evil sword's hilt, he was dragged into the mental realm. There, he was surrounded by images of the times he had fought as Nightmare and lost. Soul Calibur appeared before him, and he watched as it was swallowed up by this strange dimension where it would be slowly devoured by evil.
Siegfried's battle with his nightmares raged on. No one knows of his sacrifice. However, if there was ever one who could prevent the resurrection of the cursed sword, it would be Siegfried——he who dashed Soul Edge's hopes of devouring Soul Calibur.