Trapped in the memories of the Spark Eternal, Doctor Aphra sees how the Null Blade is not reinforced to sustain a lightsaber strike.
The Null Blade was a type of sword created by the Chadra-Fan Miril, the leader of the Ascendant, to kill the Sith. It had a cortosis alloy, which allowed it to neutralize a lightsaber, though it only worked temporarily. As of a result of Miril lacking the materials to finish the Null Blade, it was not reinforced, so, if the weapon was struck by a lightsaber, the blade broke. All the same, the Null Blade did succeed in temporarily shorting out the lightsaber that hit it. Eventually, Miril and the Ascendant were killed by the Sith, and the Null Blade was left unfinished.
Between 3 ABY and 4 ABY, after possessing the body of the archaeologist Doctor Chelli Lona Aphra, the Spark Eternal, another creation of Miril's, traveled to the the Vermillion, the Fortress-Flagship of Crimson Dawn, in search of other Ascendant technology, and drew the Null Blade from an altar in the office of "The Archivist," which it used to attack Just Lucky and Ariole Yu, though they both escaped.
Sometime 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 fight, the archaeologist Kho Phon Farrus dropped a chandelier onto the Spark, causing it to drop the Null Blade. When Starros saw the Spark head to recover the weapon, she informed Farrus, who used their calling gloves, more Ascendant technology, to take control of the blade first. Farrus noted it was heavier than it looked and was unable to lift it and questioned how the Spark could. Farrus' gloves then began to act by themselves and threw their associates against a wall of the office. The Spark revealed that because it was created to interface with other technology of the Ascendant and unite it under its command, the sword had become an extension of its will and vision when the Spark touched it, and as Farrus' calling gloves had touched the blade, they also responded to the Spark. After 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 block 0-0-0's attacks. Eventually, the Spark stabbed the two droids with the sword, and both fell under control of the Spark, who ordered them to take care of Aphra's friends whilst it left with the Null Blade headed to the Ark Angel IV.
The Spark Eternal later traveled to the Amaxine Station after being contacted by Lady Qi'ra, the leader of Crimson Dawn, with an offer she thought the Spark would find interesting, as she knew the Spark hated the Sith. As the Sith Lords Darth Vader and Darth Sidious made their way through the station to the Fermata Cage, the Spark confronted the two holding the Null Blade, which by that time was able to sustain direct lightsaber blows. Dueling Vader with the blade, the Spark managed to shut off his lightsaber but then lost the battle: Vader forced the Spark out of Aphra with a Force push.