Twilight Sparkle stumbled her way through her castle, still caught in the euphoria from her session with Nurse Redheart and Doctor Stable. She wanted more from the two, but due to her sexual inexperience, she left the hospital too exhausted. They both suggested that she cleaned herself up, that it was unbecoming for a princess to smell the way she does and to have bodily fluids caked on her coat.

She entered her personal bathroom and prepared the tub by turning on the water and letting the water reach a comfortable temperature before inserting a drain plug. She gathered her mane, tail and coat care products as the tub filled.

After the tub finished filling, Twilight climbed in and laid down on her back, her head rested on the outer edge. Her thoughts wandered back to the hospital and she felt a phantom prod against her marehood. She began rubbing herself with a hoof, occasionally teasing her winking clitoris and soon felt her dick hardening. She quietly thanked Celestia that nopony was around to watch her masturbate as she used her magic to stimulate her added package. Her magic wrapped around the base of her stallionhood like a ring and she slowly raised and lowered it.

Twilight closed her eyes and let out a quiet, shuddering moan as she continued her ministrations. Until today, she wasn't a sexually active mare, but Doctor Stable and Nurse Redheart helped her open that door. That first experience seemed too quick for her and masturbating in the tub felt like a natural thing and made a mental note to routinely do it.

Twilight felt a familiar sensation, one that she connected to her impending climax, she bit on her lip to muffle her orgasmic cry. Her spunk shot out of her rod and into the air. She caught it with her magic. She brought the substance closer to her face and examined it. It was clear and had a musky, not unpleasant odor. She recalled hearing stories that it was a fetish for some mares to ingest stallion cum and was curious about what she tasted like.

Twilight reshaped the magical container to the form of a tea cup and brought it closer to her muzzle. Ignoring the electric tingle of the magic, she tilted the container and allowed the thick liquid to enter her mouth. It had the consistency of cake batter, the taste wasn't as sweet, but it wasn't unpleasant either. She thought back to one of Pinkie Pie's ramblings, something about the taste of... “foal batter” as she put it, was dependent on the stallion's diet. Twilight would have to experiment at a later time. With the last of the ejaculate ingested, she reached her magic for the first of her mane care products, she figured it was time to start cleaning up.

Twilight finished drying off and left the bathroom, heading back to the throne room. She glanced around, making sure that Spike was still gone. It was odd having such a large castle with nopony around: no guards patrolling; no maids to keep the rooms clean; nopony. Once she knew the coast was clear, she conjured up Cadance's book and began reading.

Twilight hadn't paid attention to the cover last time, but when she did, confusion spread like wildfire in her brain. The tome was titled “1000 Spells to Improve Your Sex Life”, written and compiled by Princess Mi Amore Cadenza. At first, Twilight wanted to find a counter-spell to the penis growth spell, but could not help but read the table of contents: gender swap; sensory enhancement; erection maintenance, and a whole lot of other absurd spells.

Twilight had been so absorbed in her sister in-law's tome that she hadn't noticed two sets of hoofsteps approach her throne. Her concentration broke when she heard a giggle. She snapped the book closed and saw her brother and his wife. “Cadance!”

Princess Cadance unstrapped her saddle bag and set it on the floor as Twilight trotted to her and the two performed their ritual dance. Meanwhile, Shining Armor couldn't help but notice the new appendage between her legs. “Twiley! What the hay is that?” He said, pointing between her legs. “Is that-?”

Cadance giggled and looked to her husband. “A horse cock? Yes.” She looked back to Twilight with a grin on her face. “So? What do you think of my gift?”

Twilight fell onto her haunches, crossed her forelegs to hide her member and blushed furiously the whole time. “It's... different. How long does the spell last? I cast it last night before I went to bed.”

The princess of love gave her sister an assuring nod. “It takes roughly eight hours for the transmutation spell to complete, then you have another twelve hours of use before it goes away. Have you had a chance to use it?”

Twilight lowered her head in embarrassment. “I have. I had an appointment for a physical earlier today, but there were... distractions.”

Cadance licked her lips in anticipation. “Give me all the juicy details.”

Shining Armor's jaw almost fell to the floor. “Cadance!”

Cadance waved a dismissive hoof at her husband's objection. “She's a big mare, Shiny. Let her tell her story.”

Twilight's body got even warmer, not from potential arousal, but from embarrassment. “I... I'd rather not.”

Shining Armor laid a foreleg on his sister's shoulder, trying to comfort her. “It's okay, Twiley, nopony's forcing you to say anything you don't want to.” He took his leg off and put it back on the ground. Their eyes met and he gave her a warm smile. “Besides, your sex life is your own business, nopony else needs to know.”

Twilight smiled as a tear forced its way out of her eye. “Thanks, B.B.B.F.F.”

Cadance let out a quiet gasp and darted her head around. “What time is it, Twilight?”

Twilight raised a curious eyebrow. “Eleven thirty. Why?”

Cadance nodded. “You should be getting a sister any minute now.”

Shining Armor's eyes widened and his irises shrank in a horrified realization as he turned his head to his wife. “Cadance! What did you do?!”

Cadance playfully nuzzled her husband. “I cast a gender-swap spell on you and the penis-growth spell on myself. It should take effect pretty soon.”

Cadance was not joking, soon after she said it, the two started floating in the air and a white light began to cover the two. While Cadance wore a grin on her face and her eyes closed, Shining Armor looked terrified at what was happening to him. Twilight had to cover her eyes as the light grew brighter. Soon, the husband and wife were completely engulfed in the magical light and a loud popping sound like a firecracker emanated from the two and they settled back on the ground.

Shining Armor fell flat on the floor and rubbed his slender foreleg on his rounded muzzle. “Cadance!” He yelled in a higher pitch than he was used to. The new voice caused him to cover his mouth. He looked to his wife and couldn't believe what he saw.

Princess Cadance didn't seem to have changed, but one look down showed the she was just as endowed as Twilight. “I haven't felt like this in ages.” She said with a husky moan as she fondled her balls. “Change is good every once in a while, don't you think?” She said, maintaining her grin as she looked to her dumbfounded husband.

Twilight galloped to her now-sister. “Shining! Are you alright?”

Shining Armor examined himself. “I... I think so, but...”

Cadance tittered. “Come on, let's go to Twilight's room. We have a lot of work to do.” She said with a seductive wink.

Cadance fell on her back onto Twilight's bed and waved a hoof, beckoning Shining Armor and Twilight to join her. Her husband and sister in-law crawled next to her and Twilight began running her tongue along Cadance's shaft. Shining tentatively ran his tongue along as well. Hearing a pleasured moan escape his wife's lips encouraged him to continue.

Twilight took Cadance's rod into her mouth and bobbed her head as her brother continued licking the shaft. Cadance gasped and moaned. “Twilight! I didn't know you could give head. You're a natural.”

One last touch from Twilight's uvula triggered Cadance's orgasmic release into her mouth and on to her hoof. Twilight used her magic to coax more of her sister in-law's baby batter into her mouth. Once the last of the spunk was deposited into her mouth, Twilight pulled away and pressed her lips against Shining's. Despite his protesting, his mouth opened, as did Twilight's and his mouth became flooded with the warm fluid.

Cadance gave the two a playful smile. “Pick him up, Twilight.”

Twilight gave her sister a wicked grin, fired up her horn and lifted her brother-turned-sister. Shining Armor yelped and tried struggling against his sister's magic, but found that it was much stronger than he imagined it was and he soon found himself floating above his wife and sister, facing the latter.

Cadance waved a hoof at Twilight as she spread her legs, signaling her sister to approach her. The idea she had made her even wetter than before. Twilight made her way to the princess of love and laid herself back, propping herself up with her forelegs.

Shining's eyes widened as he witnessed his sister and wife locking their hind legs together and grinding their pussies together. The lewd sounds that emanated from the two made his heart pumping faster. His mind was telling him the sight was wrong on so many levels, but his body told him otherwise. “What are you two up to?!”

Twilight felt something wet fall onto her leg. She looked upward, continuing to grind herself against her sister. “I... I think my... big... sister is-AH! Is ready.” She said in between pants, grunts and moans.

Shining found himself being lowered. His mind halted upon realization that he was going to be fucked in two holes at once. “No! Twiley! Cadance!” His pleas went ignored and he felt two horse cocks prod both entrances. “Twiley! Please!” All she did was grin at him as she forced him further down. He threw his head back and let out a mixed scream of pleasure and pain. Pleasure from being filled in two holes and pain from the tearing in one of the holes. “Oh, Celestia! I should've been born a mare!”

Cadance and Twilight giggled. “Does my hubby like this?” Cadance said with a sultry moan.

Shining bit down on his lip and nodded as he was being hoisted, dropped and rocked back and forth along the two cocks. “Oh! C-Cadance! Th-ohhh... this is wonderful!”

The lewd schlicks emanating from the scissoring sisters and the doubly penetrated Shining Armor set the trio teetering on the edge of orgasm. Twilight's breathing became ragged as she moaned more frequently. “C-Cadance... I-AH! I do-don't know h-how-OH! Much l-longer I can last!”

“I'm almost there too, Twilight!” Cadance's horn flared and shot a burst of magic into the air, briefly enveloping the three sex-crazed mares in a bubble. The effect of the sensory enhancement spell was nigh instantaneous as the bliss-filled screams became more heated.

Shining felt it too and his body began writhing in pleasure uncontrollably. “Oh, fuck! Cadance! Whatever you did-” His thoughts were interrupted as raw pleasure overloaded his senses. “I-I'm cumming!”

Twilight pushed her new sister as far down onto her and Cadance's cocks as possible and the three mares screamed in unison. Vaginal juices exploded and spunk shot deep into Shining's holes. Shining used his sister for leverage to rock himself back and forth, his tight sphincter and snatch overflowed with their cum and he wanted more. Twilight lifted him off, triggering a second wave of orgasms to hit the trio.

Cadance and Twilight's cum shot out and struck Shining's body, coating him with their baby batter. A mixture of semen and marecum sprayed out of Shining and all over his sister's upper body, getting some on her face and in her mouth. Cum drained out of his sphincter and pussy and fell onto the bed.

Shining Armor was gently set back onto the bed and his wife and sister snuggled next to him. The trio was exhausted from their crazy fuck session and were afraid to stimulate themselves more without triggering more orgasms.

Shining was the first to speak after catching his breath. “Cadey... that was amazing.” He panted. “Why haven't you told me about that tome a long time ago?”

Cadance stroked her husband's cheek with a hoof and gave him a quick peck on the lips. “I was afraid of what you would say. That you would think I was weird...”

Shining laughed. “That, while weird, was fun as Tartarus. I'd love to continue, but... I'm too tired.”

Twilight giggled. “Me too. Besides, I think my penis is getting sore from all the sex I've had today.”

Cadance nodded. “We should rest for a while and then clean up.” She examined the bed around them. “Then maybe get you a whole new bed and sheets.” She set her hoof onto the sheet and quickly lifted it up, cum and marejuice dripped off of it. “I don't think this will be coming off.”

Author's Notes:

Whew! That one took a lot out of me. Hope you guys like Twiningdance.

Coming ASAP: Twimacinjack