A/N: Time for a little "what if" Dark Rey based on some art flying around the internet.
It was no wonder Rey was exhausted. She was curled in a ball, snoring softly in Ben's dark grey sheets. Ben watched her in wonder as she slept more soundly than he'd ever seen a human do. How she even managed to achieve sleep after everything was beyond him.
Rey's fall to the dark side was immediate and spectacular.
Truthfully, Ben never saw it coming. Sure, there was conflict in her, but as stubborn as he was to not come crawling back to the Resistance, he never expected Rey to give in to his constant pestering that she join him. Now the Sith throne would be theirs.
One night she appeared in his quarters covered in blood and reeking of raw power. Her staff was newly adapted into a dual ended red saber. Her Jakku attire was tossed out for dark pants and tunic. Her hair? Well, that was the same. Ben didn't ask anything. Suddenly she was there, traveling into his quarters through the Force bond – was that even possible? He still wasn't sure – pressing him against a wall and kissing him hungrily. There was no question she'd given in. Darkness swirled around her completely and the power was almost alarming.
When they woke that next morning, smelling of sweat and hardly well rested, Rey smiled as she gazed down at him.
Ben touched her cheek, shocked that she was still truly there in the flesh. "I knew you'd come."
She leaned in to the caress, then hesitated. Her eyes flashed. "You're… still conflicted." She drew back in surprise and sat up. "Ben. This is who we were born to be." Something in her very features had changed. "You begged me. You pleaded for me to join you. Now that I'm here, you're afraid of me?" she growled. Her teeth appeared briefly as fangs and Ben recoiled.
"What did you do?" he gasped. The soul splitting deeds he'd reluctantly performed to commit to the dark side flashed in his mind. None of them had been enough. Somewhere deep within, the light still burned and refused to be snuffed out. Even killing his own father hadn't sealed his fate. Yet in one fell swoop, Rey had extinguished her light entirely. "What did you do?" Ben repeated. There was a growing space in his chest as fear gnawed away at his composure.
Rey shrugged slightly. "What's it mater?" With that, she'd gotten out of bed and gone about her day as if she hadn't just dropped in, a completely changed person.
A week had gone by without another mention of why she was at his side. Sensing her power, the First Order had simply accepted her as his equal. Now as Rey slept in his bed – their bed – he looked down on her and gently grazed the surface of her mind. Exhaustion. Relief. Belonging. Home. He pulled out of her thoughts and pursed his lips. He'd certainly never felt that way about the First Order or even the dark side. He always felt more like a scoundrel tapping into something that wasn't meant for him. The thrill of the taboo had worn off some, but this never felt like home.
Rey rolled over and sighed softly. He loved her, but she was right. He feared her, too. There was a time that he knew in his heart and mind that she loved him, even if that love pulled her soul in two between the light and the dark. Now that certainty wavered. Suddenly Ben understood how Luke felt when he recognized the darkness in him. He glanced toward his saber on the night stand. He could never, even if she was truly the dark monster he sensed her to be.
Ben understood something else: if he got in her way, Rey would cut him down in her thirst for unlimited power.
It was time to announce the new empress to the Sith Eternals. Ben fantasized about the day for years. They'd be clad in dark, tapping in to whatever power served them. Rey would be by his side and they would change the galaxy to their liking. Now his stomach churned at the thought of Rey sitting on the Sith throne. He could handle it. He groomed himself to be the fallen prince. Rey, though? There was no telling how she would react. Her Force awakening hadn't been so long ago, and with her Jedi training and Sith heritage colliding in her very being, there was no telling how she would react. His own story taught him that.
There was no ceremony, no pomp. There was a shift in the Force that everyone felt. It was time, and they were rulers of the dark. A crowd of hooded loyalists began chanting softly. Rey's eyes sparkled as she glanced around the stone arena. Exegol wasn't a welcoming place, but she seemed to adore everything about it. Electricity roiled over Ben's skin as he watched Rey soak in the devotion. "Are you ready?"
"I was born ready," she whispered in anticipation.
"Your throne," he said, gesturing to the stone seat.
"That's not how my vision went," Rey said with a small smirk. She gave him a light push into the throne. When he was seated, she perched on his lap.
He pretended not to be ablaze at their closeness. There was something different about their bond now. Primal. Nonsensical. Urgent. Instinctual. Like life itself. Ben felt half sick, half elated. The Force between them was ablaze. It frightened him, but Rey's waist was solid under his fingertips. He let his other hand rest on her thigh. She was real, she was here, and it would be okay as long as that was true.
"This was my vision." She turned that sultry gaze to him. Her lips were full and rosy. She leaned in, dragging her lips along his long neck. "Maybe I took so long to claim my throne because I liked hearing you beg." Her fingers dragged up his thigh.
He chuckled. "Easy."
A wicked smile on her face, Rey nestled into his lap and wrapped a slender arm around his shoulders, pleased to be in view of the entire Sith following. She played with a tuft of hair over his ear.
Nearby General Hux stood at attention, a thousand yard stare not betraying the obvious discomfort that radiated from him. Was it their affection, or the hundreds of hooded figures? Ben know Hux kept a blade in his sleeve and another in his boot. If things went awry, they would be little help to the man here.
Chanting began to rise higher and louder through the large temple.
"I've heard this," Rey breathed. "In my dreams." She closed her eyes and tipped her head back, breathing deeply. "Yes." She stood. Something in the room changed. Static energy electrified the air and made the hair on Ben's neck stand. With her head still tipped back, Rey raised her arms to each side as if absorbing the strange darkness growing thicker by the moment. The chanting became less clear as the loyalists started to murmur.
"Rey?" Ben mumbled.
Her chest was heaving now and lips spread wide in rapture.
This was wrong. Ben's own chest began to heave as he struggled to regulate his breathing. He looked frantically to Hux. The general was already staring in his direction, eyes wide. Something is wrong, Hux's body language was screaming. Ben felt it. Something in the Force was shifting. Ben was being shorn down the middle. He wanted to call out to Rey, but she was in another dimension, standing perfectly still yet somehow changing before them all. Agony spread through Ben's body and he gritted his teeth and pressed his eyes shut until the feeling passed.
When he opened his eyes, Ben was shocked to find he was slumped over the side of the throne, Hux at his side. "What's wrong with you?" he spat. "What's she doing?" He glanced around the arena, which was becoming more lively by the moment.
Ben caught his breath. Something had been ripped from him. What was it? He closed his eyes, then immediately realized it. The Force bond.
Something had passed over him and entered Rey. His own darkness had been ripped away as Rey channeled it into her. Kylo Ren was gone. He felt clean. He felt whole. Ben Solo was nothing but a trespasser here in this dark place.
"Rey," Ben barked. "What are you doing?"
Rey didn't pay him heed. She'd finally let her arms drop back to her side. Her suddenly soft gaze was on the hooded figure moving slowly toward her. The loyalist carried a large chest in her hands. The Sith artifacts and weapons they'd guarded for years were now being surrendered to them, the new Sith emperors. The loyalist bowed deeply, then offered the chest up to Rey.
"Rey," Ben called. "Don't."
She turned and hissed at him, her teeth once again a row of fangs and her eyes a fluorescent amber. After a lingering sneer, she turned her attention back toward the chest.
It was over. Ben took a brief moment to center himself. He touched his light saber, but knew it would do no good. Ben looked at Hux. "Run."
Hux stared in surprise. "Abandon my post? I-"
"Run now." Ben stood and ignited his saber. It was now or never. The Force brought them together to tear them apart. Hadn't Snoke warned that it would be his undoing? "Rey."
Fangs bared, Rey spun back to him.
"What did you do?" Ben called. "You never told me."
"I did what you wouldn't, and now I am more powerful than any Jedi or Sith." She snarled softly. Lightning fast, Rey was there behind him. She kicked him from the dais and caught him by the back of the tunic before he could hit the floor. Her strength was massive and unnatural. There was no way she should have been able to support his weight. She forced him to his knees and snatched his saber from his grip as if he were a child. Before he could react, the red blade sizzled centimeters from his throat.
"The supreme leader is dead," Rey whispered.
Ben summoned the Force, but in this place, it only answered to Rey.
There was no conflict in her soul as Rey flicked the blade across his throat.
General Hux watched Kylo Ren's body slump lifelessly to the ancient stone floor. It smoked grotesquely. Hux stumbled backward. He should have run.
Rey tossed the light saber aside. She glanced at Hux, surprised to see him there by the throne.
He cleared his throat and straightened. "Long live the Empress."
Rey smiled. "Say my name again."
Hux swallowed. "Yes, Empress."