WIP
"Come to bed, darling," Rarity coos, the object of your desire flopping heavily onto your side of the sheets.
 
Already undressed save for the collar around your neck, you smile and climb up onto her bed.
 
"Mmm," she sighs as you slip her underwear off from behind, leaving her massive, bulging balls exposed to the perfumed air. "You are by far my favorite bedfellow, Anon."
 
Rarity raises herself up on her knees, allowing you to lie down while she shuffles backwards above you, dragging her musky sack across your face. She pauses with a light moan when she feels you lick them, shivering in elation as you give in to your servile impulses. You bring your hands up and caress her seed-filled balls with reverence, the soft skin giving way under your gentle touch.
 
"Hmmm," Rarity murmurs in satisfaction. "You know how to show a mare a good time… Good boy."
 
At her encouragement, you can scarcely contain yourself. Your hips make jerky, unconscious thrusting motions off the bed as you bury your face between Rarity's gigantic balls, licking every little contour you can reach while she utters little sighs and moans of pleasure. You can hear her voice getting deeper and lustier the longer you're under her, until finally she can take no more teasing.
 
"Okay, Anon," she pants, lifting herself off your face and looking down at you with an eager grin. "You know what to do."
 
You obediently extricate yourself and sit up, treating yourself to the sight of Rarity's enormous, throbbing marecock at full stiffness before crawling forward on all fours. Bracing yourself against the headboard, you spread your legs and arch your back, presenting yourself to your mistress.
 
"Good boy," Rarity purrs, moving forward to take ahold of your rounded butt. You've worked hard to fit Rarity's taste in boysluts, and your effort shows. Her hands delicately explore your body, caressing and rubbing you where she pleases. "Mmm," she sighs, leaning forward to whisper sensually in your ear. "I hope you didn't think I was going to allow you to sleep tonight."
 
She gently pushes down on your upper back, burying your face in the pillows before repositioning herself. She bucks her hips once, and you feel her gargantuan marecock slap against the skin of your stomach and chest. Her endowments practically dwarf you, and it's only through judicious use of magic that you even live to tell the tale after she's rutted you properly.
 
"Do you like feeling me, Anon? Imagining how it's going to feel when it's inside you?" Rarity teases, and you can hear the genial smile in her voice. Despite her overwhelmingly masculine prick, she's always a very affectionate, kind and feminine lover. When she's rough, it's because she knows you want it even more than she does. You reach under yourself and give her length a loving stroke, earning a husky moan from behind you on the bed. You can feel how amazingly hard she is, testament to her eagerness. You're intimately familiar with every vein, contour and bump along the surface of her proud length, and just the thought of feeling her stretching you out has you alight with need. You shake your ass in her face, a gesture that makes her giggle.
 
"Alright, alright," she says, squeezing your butt tight. "You did service me so well earlier, after all. I suppose you've earned this."
 
She pulls back to align her giant, flared cock with your asshole, its heavy length slowly sliding down your lower back until the flare catches between your cheeks. With a whispered spell to ensure your safety, she pushes forward. You can feel her flare slowly forcing its way inside, your breathing shallow as you try to relax and let the mare take you. Both of you utter groans of satisfaction when the tip is finally swallowed by your body, your asshole stretching taut around it and squeezing down.
 
From what you know of breeding stallions, the way penetration works is that they're generally two-pump chumps, seeding their mare as soon as they're inside in the interest of efficiency. The way Rarity fucks you is anything but. She loooves to take her time, enjoying the feeling of you wrapped around her massive prick, your asshole milking her quaking balls of their liquid weight over and over. She really does have the stamina to fuck you into the bed all night long, to keep you riding her marecock and singing her praises until after the sun comes up.
 
Rarity slowly slides herself further in, treating you to the sensation of her flare rearranging your insides, making you feel like you're intimately wrapped around her. You've never known if it's a side effect of the magic or just your own tendencies, but the further she gets inside you, the more you lose yourself in the feeling. By the time she's halfway in, you're groaning and right on the verge of cumming into the sheets. She pants, taking a momentary break before pushing her medial ring in, driving you over the edge. You moan like a slut as you feel her pop inside, her giggles ringing inside your ears as you needily jerk your hips along her rod.
 
"Aww, look at you," Rarity murmurs, rubbing your lower back. "Cumming all over me like that. Anyone would think you enjoy this more than I do."
 
Placing her hands around your hips, she gently rides you through your orgasm, somehow always rubbing just the right spot to make you moan in ecstasy. With a shudder, you paint your own stomach and chest in white before finally relaxing, breath coming in gasps. You can feel the soft, warm weight of Rarity's breasts come to rest on your back as she works the thickening base of her cock into you. She sighs in contentment as she lies atop you, balls-deep in your ass.
 
"That looked like it felt good, Anon," she whispers, affectionately brushing a strand of hair out of your face. "I do so love seeing you in the throes of passion."
 
She kisses the back of your neck before sitting up, putting her hands on your shoulders. Knowing what's coming next, you bury your head in the pillow. Drawing back, she pounds her wide hips into your butt with a loud smack. You whine quietly into the linen, squeezing down on her prick and earning a spurt of sticky precum for your effort.
 
"Oh, you are so good at that," Rarity sighs, pulling back for another thrust. You don't get a chance to reply, the slap of her massive balls against your rump silencing any words you could have mustered. She begins fucking you in earnest with long, deep strokes that leave your mind reeling, each one pushing the air from your lungs in a breathy moan of subservience. It feels so good to lie here and just take it, to be used as an outlet for Rarity's lust. You can feel the skin of her cock being pulled taut every time she takes you, the swollen flare stretching you out around it.
 
"I'm getting c-close, Anon," she pants, her thrusts picking up in pace. Within moments she's practically slamming you against the wall, hands pulling your legs apart as she loses herself in her need. Droplets of sweat from her shaking breasts land on your back every time she pounds you, her honey-sweet voice rising in volume until she finally cries out in joyous release. She collapses on top of you, her hips bucking frantically as she empties her swollen balls into you. You can actually hear as well as feel her hypersized testes working overtime to fill you with spunk, each little twitch and jerk of the moaning mare accompanied by a massive gout of sticky cream. Warmth blossoms from your centre, radiating outwards until it feels like you're floating on a fluffy cloud of bliss.
 
Rarity nuzzles at your neck and nips at your ears with sultry little growls while she pumps you full of marejizz, her orgasm continuing for what feels like minutes before the gurgling of your stuffed tummy starts to subside, finally filled to capacity. The excess spunk begins to splatter down your quivering legs, running down your behind and coating you in her seed. You can't help but moan at the sensation, feeling for all the world like you've been bestowed the best gift you could possibly be given.
 
"Mmmmm," she sighs in your ear, running a hand down your side and giving your butt a little spank. "Your ass always feels so good, Anon. I know you like to keep it tight for me."
 
You surprise her by twisting around to give her a kiss, locking lips with the beautiful mare. You can feel her cock twitch inside you before she leans into it, possessively grabbing your neck. She starts pounding you while kissing, moaning into your mouth with desperate need. You've really stoked her flame now, the horny mare not likely to stop now that you've shown her how much you want it. You curl your legs around her voluptuous thighs, all but begging her to take you in her desire.
 
Rarity obliges you without hesitation, bouncing on top of you as her lower half feverishly bucks and jerks, driving her iron-hard cock further in. She pulls back from your passionate kiss and hugs you around your midriff tight enough that it almost hurts, keeping you from moving under her while she rams you again and again. She doesn't even notice you cumming again, the violent movements of her fat prick too much for your prostate to bear. A never-ending dribble of spunk flows from your dick and soaks into the sheets, each thrust forcing another string of cum from your balls.
 
You smile dopily into your pillow, crying out in slutty pleasure as Rarity makes you her bitch. The sound of her balls slapping against your ass is so loud you wouldn't be surprised if a pony flying by could hear it, and you wouldn't care if they did. You'd let her fuck you like this in the street if she wanted, and the harder the better. The constant prostate orgasms are only half the fun; the other is being a literal outlet for Rarity's lusts. From the moment you met her, your thoughts were occupied with the idea of serving as this voluptuous mare's depraved sex toy. She treats you nicely, but you love it most when she lets loose, overcome by her hyper-proportioned sex drive.
 
Luckily for you, it really doesn't take much prodding for her to give in to her animal urges. Right now she looks - and fucks - more like a bestial wild woman than the pretty, fashionable mare everyone else sees. She's focused on nothing but busting a massive nut inside your tight, warm hole. You wouldn't mind holding on to this feeling forever; ultimate submission, a cumdump for her beautiful, throbbing marecock.
 
"Oh god," you gasp, feeling a second orgasm arriving right on top of the one you're already in the middle of. "I-I'm gonna-"
 
"Are you cumming, Anon?" Rarity pants, not slowing down for even a second. "You gonna cum all over my fat cock and get my sheets dirty? What do you say to your mistress?"
 
"Harder," you manage to get out, your voice barely above a whisper.
 
"What's that, Anon?" Rarity asks. "I didn't quite catch it."
 
"Fuck me harder!" you lustily moan. "Please!"
 
"And who's my bitch?"
 
"I'm your bitch," you whine.
 
"Good- mnnn! Boy," Rarity says approvingly, slapping you on the ass. You cry out in pleasure, the stinging red mark just another reminder of who owns you.