Disclaimer: Star Wars and all related characters, names, etc. are property of Lucasfilm, LTD. Star Trek, The Borg, and all related indicia are property of Paramount Pictures, Inc. The author does not have the permission to use either Star Trek or Star Wars in this fic, and is making no money from writing this.
Note: This fic is the second part of the story I wrote in "The Borg vs. The Empire Part I: The Death Star" (available here on FanFiction.net).
Prologue
It is three years since the Borg first arrived in the galaxy and confronted the Empire's ultimate weapon, the Death Star. Although the Death Star had temporarily defeated the Borg's plan to invade Coruscant, the Borg escaped, leaving a few of their own on the massive space station. The small collection of drones transported over to the Death Star with orders to assimilate the space station. Those drones were subsequently destroyed by the dark powers of Darth Vader, Lord of the Sith.
The surviving Borg included both the Borg Queen and her new mate, former Grand Moff Tarkin. They diverted their course from Coruscant in favor of a more secluded, more easily acquired target: the Maw Installation, a weapons research facility established by Tarkin himself. It was there the Borg could secretly build up their forces while assimilating the latest military technology in the galaxy.
After Darth Vader destroyed the Borg assimilating the Death Star, his sudden saturation in the Dark Force helped him see something that he had not before: Leia Organa, his royal prisoner, was his biological daughter. He confronted her with this information, and using her natural aptitude with the Force and her anger toward him, gradually seduced her to the Dark Side.
Thanks to Vader's new control over Leia, she revealed the location of the secret base of the Rebellion, on a moon orbiting the planet Yavin IV. However, unbeknownst to Vader, a motley group of adventurers, led by Vader's old master Obi Wan Kenobi, had already delivered blueprints of the Death Star to the Rebellion. The Rebels found a weakness in the supposedly invincible battle station, and were ready with a fleet of starfighters when the Death Star arrived at the Yavin system.
Vader, immediately detecting a pattern to the fighters' attacks, took his apprentice with him in his prototype TIE fighter as he attempted to stop the Rebel fighters. However, Vader was foiled by the interference of Han Solo, a spice smuggler who had been hired by Kenobi to assist them and the Rebellion. With Vader's ship momentarily disabled, a particularly strong Force-adept pilot fired two proton torpedoes down an exhaust vent into the Death Star's power core, detonating it and obliterating the space station.
Meanwhile, the Borg built up their fleet, preparing.
Vader, his pride as damaged as his ship, fled from Yavin with his daughter. Despite Vader's failure to stop the Rebels, the Emperor granted Vader command of the entire Imperial fleet and sent him on a mission to eradicate the Rebellion once and for all. Leia Skywalker accompanied her father, and as time passed, she learned more and more of the power Vader intended for her use to rule over all lesser beings.
Unaware of any existing Borg threat, the Empire has become complacent in their feeling that their resources are properly allocated to hunt down and fight what they saw as their only real opposition. What it doesn't know, though, is that the Borg are about to return, their goal being total control over the galaxy. Whatever the cost.
This time there may be no stopping them…