- "For whomsoever takes up this blade shall wield power eternal. But just as the blade rends flesh, so must power scar the spirit."
- — An unknown spirit speaking to Cadden Blackthorne
Soulblade was an ancient Sith Sword that the Nomad Soul created during his time in the mortal realm. The exact nature of Soulblade was uncertain, but it was discovered that the Nomad Soul intended that Cadden Blackthorne – his unwitting potential host – would discover it.
During the climactic finale of the Battle of Onderon, the Nomad Soul once again spoke to Cadden in his mind. He told him that, alone, he could not hope to counter the great power of the one who killed Faarel Blackthorne. He instructed Blackthorne to set out and find Soulblade, and claim it. Doing so would grant him a great deal of power.
The Nomad Soul was counting on Cadden's state of anger and hatred toward the Cult of Shadow, particularly to Faarel's killer, to fuel his desire to search for the blade. The plan worked, and Cadden blindly followed the command set forth by the Nomad Soul. Zan Fyar, Cadden's former apprentice and now Jedi Knight, aided Blackthorne in his quest, in an attempt to sway him from the Dark Side.
The two individuals traveled to the Unknown Regions, Blackthorne blindly following the blade's call, until he reached a desolate world. There, he sought out and discovered the blade, buried in a sealed box. Before he could access the blade, however, several spirits appeared before the two Jedi, whom tried to warn Cadden of the danger. Cadden dismissed their warnings, and used the Force to break the box and, claiming Soulblade, he cast aside his own two lightsabers.
With the sword in hand, Cadden set out, with Zan at his side, to hunt down the culprits of his father's death. Fyar could feel the Dark Side energies teeming from the blade, and the more he sensed them, the more corrupted he, too, became.
However, Soulblade had other plans. The more Cadden possessed the blade, the more he submitted to its will. The voice of the blade promised him great power, and through that power, Cadden's revenge. However, Blackthorne had to make his own sacrifice, for his vengeance.
Cadden followed the blade's calling through the Unknown Regions, to a barren, rock and sand world. There, he sought an ancient tomb. Zan, feeling the Dark Side energies within, warned Cadden of the dangers.
- "If we pass beyond these doors, we can never go back. The Order will surely banish us."
- — Zan Fyar
Such words did not dissuade Blackthorne from continuing through the door to the tomb within. Though a part of Fyar yearned to return to the Jedi Order, he remained at his friend's side, knowing that once he crossed the threshold, there would be no chance of ever going back to the life he once had.
The two entered a burial chamber, deep within the tomb, whereupon a voice whispered into Cadden's ear, telling him to destroy the ancient stone sarcophagus. Blackthorne, now corrupted by the blade's power, obediently followed, thus released the spirit of the Nomad Soul from its prison. The spirit entered Cadden's body, and the two souls formed into one being.
- "Now, I am complete."
- — Cadden Blackthorne, after the merging of his soul with the Nomad Soul's
- "Death and darkness are all that await you here, Jedi."
- — Unknown spirit speaking to Cadden Blackthorne
Soulblade had the ability to drain life from its victims, and to drain the soul of anyone whom it connects to. The Nomad Soul was capable if seeing through the eyes and hearing through the ears of anyone who wielded Soulblade, an ability that could only be ceased by the strongest of Jedi Masters or Sith Lords. Able to communicate to the wielder telepathically, on any plane over any distance, the Nomad Soul used this ability to try and corrupt the wielder over time.
An individual who wielded Soulblade would not part with it willingly and, over time, even the strongest of wills would be broken by the corruption inherent in the blade and its creator. After which, the individual would become a servant to the will of the Nomad Soul, so long as they remained within ten kilometers of the weapon. Beyond this, the sword could not control the wielder's body, and the wielder would become aware of their current state (if they were not already).
If the person were to come in contact with both the weapon and the Nomad Soul's sarcophagus, the Nomad Soul would thus enter their body and either destroy their soul, or merge with it, depending on how willing the host would be. If the soul were to merge with the Nomad Soul, the Nomad Soul would thus gain all the skills and memories of the victim, while granting his inherent knowledge to the host. This has only happened once, with Cadden Blackthorne.
Whether these effects are permanant, or can be reversed, are currently unknown.
Furthermore, Soulblade had the ability to strike incorporeal creatures as though they were fully corporeal, and had the ability to transfer the lifeforce from its slain victim to its wielder.