Shortly after the Battle of Yavin, Doctor Cylo and his fleet attempted to hijack the Executor-class Star Dreadnought Executor while the flagship was still under construction in the Kuat system by the shipyards operated by Kuat Drive Yards.
During the War on Shu-Torun, Doctor Cylo collaborated with the rebellious ore-dukes in an attempt to kill the Dark Lord of the Sith, Darth Vader. However, the Sith Lord survived and led the Empire to victory. Morit Astarte had killed his sister Aiolin Astarte, as she was a competitor to him in supplanting Vader, and he fled with Cylo and Tulon Voidgazer. After this, the Dark Lord would be sent by his master to hunt them down. Meanwhile Vader sent his two assassin droids 0-0-0 and BT-1, to capture Doctor Chelli Lona Aphra and bring her to the Executor, as she knew about his plot against the Emperor. The Dark Lord took the Devastator to the Crushank Nebulae where he led TIE fighters in an attack on the rogue scientist's fleet. Cylo escaped, but not before Vader got aboard his flagship. He went through the labs and was eventually confronted by Voidgazer, who pitted him against her cyberanimate rancor. However, this opponent was no match for Vader, who slew the beast before killing Voidgazer herself.
As Vader was fighting Voidgazer, Cylo's fleet emerged from hyperspace. On the bridge of the Executor, Grand General Cassio Tagge ordered the batteries to open fire. However, they found the weapons, doors, and controls offline and watched in horror as sleeping gas emerged from the vents and knocked them out. In the Emperor's throne room, a Royal Guard informed him they are operating on their own life-support system. In a last ditch effort, Cylo and Morit abandoned their flagship and set it on a collision course with the Executor. Vader reached the bridge of the vessel to stop the collision course, but found that it couldn't be altered.
Aboard the ship, Cylo's forces found the crew knocked out and took over the bridge. They then activated ion charges to disable pursuing vessels. However, before they could escape, the power went out. The Dark Lord of the Sith then contacted them and revealed that he had cut the power and that he was coming for them. Morit went to deal with Vader while Cylo's troops went to capture Palpatine.
Morit jumps at Vader on the hull
Meanwhile, Aphra had used the programming of BT-1 and 0-0-0 to get them to help free her: Vader's priority order to both droids was only to bring her aboard the ship, so, with that done, she could give a new priority order that they help her. She decided that in order to get Vader off her tail, she had to report his plot to his own master, Palpatine. She alongside the droids, and the Wookiee bounty hunter Krrsantan, who was there because she owed him a great deal of money, went to defend the Emperor from Cylo's troops. Morit met up with Vader on the hull where they dueled. The Dark Lord Force-pushed his adversary onto a ledge where he regained balance, only for Vader to destroy it with the Force, killing Morit.
As the Emperor's Fist approached the bridge, the troops sent to capture the Emperor withdrew and went after the cyborg, who cut them all down. When Vader arrived at the bridge, Cylo reminded him he was his machine as he deactivated him with a button. Knocked out, Vader had a vision in which he returned to Mustafar and killed Obi-Wan Kenobi and Anakin, then choked Padmé Amidala. He then stated Skywalker was dead as he awoke, shocking Cylo. Vader then stabbed Cylo-V and killed him. Aboard Cylo's whale fleet, Cylo-VI awoke desperate to escape. The Dark Lord departed in his TIE Advanced x1 and informed his master that the ship was under Imperial control as he raced off to stop the scientist's escape. Right then, Aphra barged into the Palpatine's chambers to explain Vader's plot.
Vader pursued Cylo as his fleet tried to stop him from getting to the flagship. The vessel escaped, but not before the Dark Lord had boarded it. He took out all of Cylo's marines and as he went through the cloning chamber, he was confronted by the clones of Cylo. As they taunted him he killed them all with ease. Vader then confronted Cylo-VI on the bridge, who still bragged that he was immortal. However, the Dark Lord used the Force to send the ship into the nearby sun and left as the ship was torn apart, permanently ending the turncoat scientist.
The Dark Lord then returned to the Executor to report his victory. Palpatine revealed that Aphra told him of his treason. Instead of being angry, he congratulated his apprentice and left him to deal with the "delightful girl". Vader ejected Aphra out the airlock and then went to meet Tagge and Palpatine on the bridge. Citing the Grand General's blunder and misplaced trust as reasons for relieving him of his Supreme Commander duties, the Emperor instead granted his apprentice absolute command of both Death Squadron and the entire Military. As soon as Palpatine departed, Tagge attempted to reason with Vader, but he was cut off and met his demise at the hands of his intolerant new superior's grip. The Emperor's Fist gave Admiral Kendal Ozzel two weeks to have the Executor ready for action. Aphra ended up being rescued by Krrsantan, with Vader now off her tail since he believed her to be dead.
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