"You say my path lies across your grave... but does your path lie across mine?"
Hunched over his desk like a gargoyle plotting mischief, Thales brooded. It was an unlikely scenario for him to be in given the recent success of Order 66, but here he was. Order 66 had taken away many of his pawns, and though he was still left with an army of totally obedient clones, he found himself pondering the issue of… not succession, for succession would imply he had any intention of stepping down from power.
No, what he pondered was more an issue of hierarchy. Much as every Sith needed an apprentice, every Emperor needed a lieutenant, someone to show the flag and deal with rebel scum and other malcontents. Yes Thales could eviscerate the perpetrators himself, but his chair-turned-throne was just so comfortable… He'd also have to leave his wine cellar.
No, the Sith Lord needed his Apprentice, the important but still expendable pawn that would inevitably try to betray him before being tossed aside like last week's garbage. The only question was who.
Solon was dead, Cornelia had died before his eyes at his own prompting, and the less said about the disaster at the Temple the better. So that just left his secret Sith, the ones he'd subjugated and augmented with ancient Sith Alchemy, and were never intended to surpass his true acolytes.
Jeritza was dead, Hapi had never reported back, and Shez and Lysithea were dead to him, which was the only state of death that mattered. Though he'd already sent the clones to hunt them down so they would be dead soon regardless.
Therefore, by process of literal elimination, that left Edelgard.
Nodding to himself, Thales opened up a channel to his new Apprentice.
"Edelgard. Now that the Jedi have been exterminated, it's time to end the war. The Separatist leaders are gathered in the Mustafar system. Kill them."
"…As you command," accepted the Apprentice after a moment's hesitance.
"But before you go..." forestalled Thales. "Have you ever heard the tragedy of Epimenides the Wise?"
The crimson blade flashed as it cut through the elite ranks of the Separatist leadership's chosen protectors, their skills and weaponry unable to cope with the raw power and brutal elegance of a burgeoning Sith lord. Every movement, every breath, brought destruction and carnage upon her victims.
The droids, dismembered. The bodyguards, bisected. The politicians, purged.
The last of the Separatists had his back to a wall as she advanced on him, his mouth blithering uselessly. "The war is over!" begged Ludwig, "Our surrender is unconditional, you- AHHH!" He screamed a final time before the lightsaber ripped across his body, the fresh corpse dropping to the floor to join the rest.
Ludwig, Gregoire, Vestra the Elder, and more lay strewn across the makeshift slaughterhouse. Standing alone in the center of it all was Edelgard,
She turned to leave, never looking back at the terrible butchery she had wrought.
"Master Rhea!"
Stumbling out of one of the Senate building's maintenance shafts, the battered and beaten Jedi vaulted out of the cramped passage and landed in her compatriot's getaway vehicle. She collapsed in her seat, finally allowing herself a small amount of relief after the disastrous fight against the Sith Lord. A valiant effort she may have given, but a loss was still a loss.
"I failed," she admitted quietly, eyes closing as she shed a single tear. "Evil now controls the galaxy, and we will be hunted by the darkness forevermore."
"Master Rhea… what should we do?"
Rhea sighed. "Drive, Flayn… Take us to the undercity. We need to disappear, then get off-world and find a place to hide."
The padawan frowned but did as she was told, expertly guiding the speeder into traffic. "Is this really the only way?"
"It is," answered Rhea sadly. "Perhaps one day we will again be able to walk in the light, but until then… our only recourse is exile."
"I yield!"
Edelgard stopped, lilac eyes wide in astonishment, mere inches away from tumbling over the cliff to the river of lava below. Before her stood Byleth, the Jedi having triumphed over her in single combat and even managing to destroy her lightsaber, thin trails of tears fresh on her face as she gazed upon her former student in horror at what Edelgard was prepared to do.
"I yield…" she repeated, softer, pleadingly. "Don't do this."
Slowly, the Sith stepped away from the cliff edge, eyes narrowing in scrutiny. She held out a hand. "Give me your lightsaber," she demanded.
The Jedi relinquished the weapon without pause, allowing Edelgard to pull it away with the Force. Her tears stopped falling as relief overcame her. Edelgard briefly considered casting aside the weapon into the lava, but that would serve no purpose other than petty spite.
She walked closer to her teacher, continuing to analyze the woman's posture for any sign of deceit, even as she pulled out a set of restraints. Byleth didn't resist as she put them on.
Edelgard turned away, hand tightening on Byleth's lightsaber. "You will regret this," she promised, certain of the inevitability.
"I would've regretted your death more," rejoined her captive without hesitation. "Edelgard… I'm not a very good Jedi. My attachment to you is far stronger than what any proper Jedi should feel for their former padawan."
"And that sentiment is your undoing!" snapped Edelgard.
"Perhaps," allowed the Jedi. "But if this is my downfall… I'm content that it was by your hand."
"How can you stand there and just… give me victory?" demanded the Sith with outrage. "I'm a killer, a murderer! And I'm complicit in the genocide of your entire order!"
"But you're still you," said Byleth. "And there is good in you. I know there is."
A spark of anger lit within Edelgard and the Sith swung her teacher's lightsaber towards its former wielder. Byleth was unflinching, retaining her hope, her affection, even as the blade sizzled only centimeters from her neck. Edelgard glared at her, knowing her path was decided since she'd undergone the procedures, since she and her kin had been subjected to those evil experimentations.
She was a Sith and Byleth a Jedi. The only proper thing to do was finish it. Yet she stayed her hand.
She didn't want to admit it, but much like Byleth, Edelgard's attachment to her was far stronger than what any proper Sith should feel for a former teacher.
Retracting the blade, Edelgard lowered her hand. "From now on, you are my trophy," she decided. "You will obey my every command and serve at my whim. Kneel if you understand."
Byleth slowly did as she was told, pledging herself to Edelgard amidst the blazing embers and burning lava flows. "I am yours, Mistress."
AN:
As products of Sith alchemy, the 'secret Sith' have abilities beyond normal Force users.
Jeritza – Extreme endurance and survivability, to the point where Byleth's killing of him is actually quite the impressive feat
Edelgard – Camouflage and concealment, very helpful for infiltrating an enemy organization; less helpful when fighting someone who is intimately familiar with her Force presence
Lysithea – Raw power and Force affinity; when compared to the Force lightning she wields, a regular Sith Lord may as well be using static electricity
Shez – Near total Force immunity, such that the Force can't be used on her nor can she use the Force; so she can't Force choke or be Force choked, Force heal or be Force healed; also can't be Force persuaded, but is dumb enough such that regular persuasion will usually suffice
Hapi – Affinity and kinship with Force-sensitive animals and creatures, not that it ever came up; in the expanded universe she gets to sic a horde of terentateks on Thales