Celestia opened her eyes, and yet the air around her felt dreamlike. She was in a sea of black, a haze of azure mixed with a royal purple spreading all around her. Her head was swimming. What had happened?
She tried to remember, but the only image she could envision was a dark shadow sliding over the moon. The mere memory sent a shiver through her, an ominous dread filling her lungs.
An icy laugh sounded behind her. Celestia turned her head to face the source. A dark mare stepped toward her, black as the night itself, with cerulean eyes that glowed in the darkness. It was Luna... and yet it wasn't. Celestia couldn't call this creature by her beloved sister's name. This was Nightmare Moon.
Celestia's horn flared to attack, but a surge of weakness filled her head. Why was she so tired?
"I wouldn't try that again, if I were you," Nightmare Moon grinned at her sister, her fangs gleaming.
"Again?"
"Yes. Don't you remember how swift your defeat was the last time you tried to challenge me?"
Celestia felt fear, deathly cold fear begin to well up within her. "This is a dream. A nightmare. It must be."
"Of sorts," Nightmare Moon replied. Her horn glowed blue, and the darkness fell away. Celestia found herself in the Castle of the Two Sisters, the throne room ornamented in blue, shadows in every nook and cranny of the room, chased away by only moonlight. She was before the thrones, one of them removed. She turned to see an array of batpony guards, all saluting their queen of darkness.
Another pulse of magic sent Celestia's forehooves to the ground. Nightmare Moon stood in front of her, towering over her older sister, and addressed her faithful servants. "Tonight is the beginning of the end for Equestria," she began. "For tonight begins a nightmare that will never end, a reign of fear that can never be broken. The darkness has given me power, my little ponies, power far beyond even that of my pathetic sister." Here, she licked her lips, her tone turning seductive. "Power greater than any stallion could ever hope to wield between his legs."
Celestia gasped in horror as Nightmare Moon turned her side toward her, revealing a black sheath from which spilled forth a midnight-blue horsecock, still flaccid and flopping, but still so very thick and long. Beneath that dangled a pair of large testicles, bigger than Celestia's hooves, swaying as Nightmare Moon slowly throbbed to hardness.
Celestia had never seen a stallion like this before, let alone her sister. Celestia had always been a holy virgin, and purity was one of the virtues she had worked so hard to instill in her kingdom. Her stallions curbed their sex drives at her wisdom, and foals were taught to be a greater priority than lewd pleasures. Already she felt a stain on her white soul just at the sight of the organ that she had only ever imagined before.
"The nightmare forces have blessed me, allowing me to transcend the form of a mere mare." Nightmare Moon hissed as her cock reached full hardness now, longer than Celestia's arm and thick as a log. The dark mare displayed it proudly. "Behold! My mighty malehood, brimming with virility! With it, I shall defile all that is good and pure! And behold, between my thighs lie the great crown jewels of this new empire! With their potent lust, greater than any male, I shall plant the seed of darkness within this land!"
Celestia grunted as she felt her chin wrenched upward, her nose inches away from the throbbing flare. "Witness my victory," she said at last. Magic once again seized Celestia's face, her jaw forced open, and the big shaft was plunged into her throat.
"Ahh," Nightmare moon purred. "You have no idea how long I've wanted to see you kneel before me, Celestia."
Tears streamed down Celestia's face as she forced back gags. Nightmare Moon's member was too thick, too long, and she felt bile in the back of her throat, her body wanting to throw up. But Nightmare Moon only thrust more, slobber dribbling down Celestia's chin as tears began to stream down her face.
"Your service pleases me, dear sister," Nightmare Moon gloated. "I shall make sure to enjoy you often, if only to see those beautiful tears of yours."
"Mmmf!" Celestia protested as Nightmare Moon began to thrust forward, her heavy nuts slamming into Celestia's collar. The good princess's muzzle was forced to Nightmare Moon's black sheath, her throat utterly filled with her vile meat.
"Oh, how my balls churn," the dark mare moaned. "You are being very good. Soon, I will give you your reward."
Celestia didn't know what she meant, but she didn't have a choice. She just wanted this to be over, to wake up. She pressed her lips around the thick flesh, stroking it with her tongue, tingles spreading through her own body with every movement.
"Mmm," Nightmare Moon hummed. Celestia's eyes widened as she felt the cock stiffen in her throat, forcing another gag from her. She had no idea what was happening, but Nightmare Moon moaned above her. "Yes, drink from me, Celestia. Taste the sweet juice from my two precious fruits."
Panic rushed through Celestia as she felt a hot, creamy liquid flooded her throat, filling her gullet quickly in powerful blasts. It was salty and bitter at first, yet musky and potent. Even as she retched at the taste, she felt heat flood her body, her lavender eyes rolling upward. It was intoxicating. Her grunts of protest quickly turned to moans as sensation foreign to her pristine body began to fill it, and she found herself gulping more and more of the thick fluid, watching the pleasant twitch of Nightmare Moon's big balls in her heavy sack as they pumped out more and more delicious nectar into her.
Nightmare Moon pulled out at the tail end, gripping Celestia's face tightly, making sure to unload a few final blasts onto her sister's perfect face. Celestia could only lick her lips, panting hotly for more of the heady fluid. Yet now that her mouth was empty, her thoughts returned. What was going on? What putrid liquid had she been forced to drink? And why was she so... aroused?
Celestia's nethers burned in a way they never had before, and the sight of Nightmare Moon's cock only made them throb. The wicked mare cackled again. "You have done well, sister. I think I have another reward in store for you." A batpony brought an ebony case on cue. Nightmare Moon opened it, withdrawing a set of black leather reins with a shining steel bridle and bit. "I shall make you my new pet, and I shall be your master, just as I am for all of Equestria now."
Her white cheeks flushed red at the very thought of wearing something so humiliating, yet her legs trembled at the word 'master.' Would Nightmare Moon force Celestia to call her that? The idea sent a thrill down her spine. A voice seemed to scream in the back of her mind, but she couldn't quite hear it through all of these confusing new sensations.
She didn't fight as she felt the leather surround her stained muzzle, and she even opened her mouth obediently for the bit. Just the taste of the cold metal on her tongue made her shiver with anticipation.
Nightmare Moon circled behind her. "Now on to the real fun," she said in a dark tone. Then, commanding, "Present yourself for my use, sister."
Celestia's tail raised immediately, revealing a hot, dripping, needy pussy. Even her flanks were angled sky-high, Celestia thoughtlessly, wordlessly begging for that great shaft to plunge into her, to relieve her of this insufferable, hellish burning.
Nightmare Moon mounted, hooking her hooves around Celestia's shoulders, taking the reins in her own fangs, yanking powerfully, snapping Celestia's head back.
"Ahh!" Celestia cried out in pain and pleasure as she felt her marehood split apart by her sister's mighty endowment, her entire body stuffed full of thick cock in one swift motion.
"So wet," Nightmare Moon moaned. "Do you wish to be bred, like a proper mare?"
Celestia fought back tears in her eyes. Her pussy throbbed around the shaft buried in it, the sensation so satisfying to her. She couldn't deny her needs. "...Yes," she admitted quietly.
"Hm. Then I shall rut you like a stallion," she said smugly.
Nightmare Moon began to fuck Celestia like a wild animal. "Nng!" Celestia cried out around the bit in her mouth. That long, thick shaft pounding her flanks was so rough, so hard. And yet, it was so good! Celestia had never felt such pleasure in her life! If only she had known a big, fat cock could bring her such ecstasy, she would have whored herself out to every male in the kingdom. Yet now, she could only rejoice as her burning nethers were fucked hard, her clit buzzing as her sister's fat orbs slapped against it. She thrust her hips back, begging with every moan and every movement to be thoroughly, roughly bred.
"You've always had such a plump, fat ass, Celestia," Nightmare Moon said, delivering a stinging spank to prove her point. Celestia's rump jiggled, only making Nightmare Moon pound her harder. "I will enjoy emptying my nuts into you."
"Please," Celestia begged, her voice muffled by the bit.
She moaned again as she felt another hard spank across her flanks. "I will make sure to hump these sweet flanks of yours in my court, so that every one of your precious subjects can see how well you take my great cock."
Nightmare Moon was pumping into her fast now, and Celestia tossed her head as the pleasure built within her, but Nightmare Moon held her down, first with a quick bite, her fangs sinking into the meat of her neck. When she withdrew with red on her fangs, sighing, she snapped the reins back once more as she addressed her guard. "My nuts ache, my loyal ponies, and my release is nigh. With it, I shall impregnate my sister, and the foal between our unholy union will be the beginning of a new generation of ponies, bred from darkness! Fix your eyes on me as the once-pure Princess Celestia is humped into submission, as a stallion would a cheap whore! Watch as I breed her, and witness the climax of my dark power!" A deafening cheer rang throughout the hall, and Princess Celestia felt her own marehood pulse, her pussy beginning to throb and gush as Nightmare Moon fucked the hell out of her. Just as her orgasm took her, Nightmare Moon called out in her own, roaring with triumph, "My subjects! I cum! Ahh!"
Celestia's mind blanked, her mouth agape as fire and ecstasy filled her, her juices spurting over Nightmare Moon's balls as they pumped gouts of boiling hot cum into her womb. Celestia's flanks bucked backward, her pussy clenching, milking her sister of every drop of seed she produced. Nightmare Moon bit down hard on her neck, thrusting hard a few more times as Celestia moaned. It was as if she could feel the seed taking root in her, making her heavy, stripping the last of her purity from her.
Celestia felt dizzy as it ended, collapsing on the floor, her body utterly stuffed full of cum. She could feel the warm cream flowing from her used, throbbing cunt, and it made her breathing heavy. Nightmare Moon's words swam through her head, and weakly, she looked up at her sister.
"Go forth, my little ponies. Celebrate this night!" she commanded, and they flew out, their dark bodies melding into the shadowy sky.
"Sister," Celestia said weakly. Nightmare Moon turned toward her pitiful form, her mane and tail a cum-soaked mess.
"Hm?"
"May I suck you cock again, master?" Celestia said. "My throat burns for your sweet cum."
Nightmare Moon grinned. She took Celestia by the reins as she took the throne, spreading her legs, leading her sister's muzzle to her softening dick.
"I am glad you have discovered your place, my pet." She chuckled to herself. "Now, pleasure me."
"Yes, master."
"Ahh," Nightmare Moon groaned. Without hesitation, Celestia plunged herself onto her dark royal stallionhood once more.