The Null Blade was a sword crafted from cortosis alloy by Miril, who led the anti-Sith Ascendant cult during the Sith era. Being made of cortosis, the weapon had the ability to temporarily short-circuit a lightsaber upon contact. However, because Miril hadn't reinforced the weapon by the Ascendant's downfall, a lightsaber could cut through the Null Blade itself. Essentially, Miril's weapon could disable a lightsaber, but at the cost of its own destruction. Many centuries later, the Spark Eternal—a creation of Miril and the Ascendant—reemerged and took control of Doctor Chelli Lona Aphra's body. After rediscovering the Null Blade, the Spark used Aphra to wield it. By this point, the blade could withstand lightsaber strikes. The Spark-possessed Aphra then fought the Sith Lord Darth Vader during the Amaxine Station battle, where she managed to short out Vader's lightsaber when their weapons clashed. Vader responded by using a Force push to separate Aphra from the Spark.
The Chadra-Fan Miril, who was the leader of the Ascendant, forged the Null Blade as a type of sword to eliminate the Sith. Its cortosis alloy enabled it to briefly neutralize a lightsaber. Due to Miril's lack of resources to complete the Null Blade, it lacked reinforcement, leading to its destruction upon impact with a lightsaber. Nevertheless, the Null Blade was able to temporarily disable the lightsaber that struck it. Ultimately, the Sith killed Miril and the Ascendant, leaving the Null Blade incomplete.
Sometime between 3 ABY and 4 ABY, the Spark Eternal, another creation of Miril's, possessed the body of Doctor Chelli Lona Aphra, an archaeologist. It then journeyed to the Vermillion, the Fortress-Flagship of Crimson Dawn, in search of Ascendant technology. The Spark retrieved the Null Blade from an altar in the office of "The Archivist," using it to attack Just Lucky and Ariole Yu, who both managed to escape.
Later, a team of Aphra's associates, assembled by the smuggler Sana Starros, arrived at the office to rescue Aphra from the Spark. During the ensuing fight, Kho Phon Farrus, an archaeologist, dislodged a chandelier onto the Spark, causing it to drop the Null Blade. Starros, seeing the Spark move to reclaim the weapon, alerted Farrus, who then used their calling gloves, another piece of Ascendant technology, to seize control of the blade first. Farrus found the blade surprisingly heavy and questioned how the Spark could wield it. Farrus' gloves then began to act autonomously, throwing their associates against a wall. The Spark revealed that, as it was designed to interface with and unite Ascendant technology under its command, the sword had become an extension of its will upon contact. Consequently, Farrus' calling gloves, having touched the blade, also responded to the Spark. Following this, the assassin droids 0-0-0 and BT-1 entered the office and attacked the Spark Eternal. The Spark used the Null Blade to parry 0-0-0's attacks. Eventually, the Spark stabbed both droids with the sword, bringing them under its control and ordering them to deal with Aphra's friends while it departed for the Ark Angel IV with the Null Blade.
After being contacted by Lady Qi'ra, the leader of Crimson Dawn, with an offer she believed the Spark would find appealing due to its hatred of the Sith, the Spark Eternal traveled to the Amaxine Station. As the Sith Lords Darth Vader and Darth Sidious advanced through the station towards the Fermata Cage, the Spark confronted them, wielding the Null Blade, which by then was capable of withstanding direct lightsaber strikes. During a duel with Vader, the Spark managed to disable his lightsaber but ultimately lost the battle when Vader used a Force push to expel the Spark from Aphra.