Twainbow: Twilight Plus Rainbow Equals This
Author's Note
Second clop story, hope you like it.
It's kinky and fucked up, just my style! 
Edit: Left some room for a sequel, if people want that.
Let The Twainbow Begin!
"So, I'm supposed to put this on my horn..?" Twilight questioned, giving her marefriend, Rainbow Dash, a quizzical look. "And use it to... make love to you?"
"That's the general idea, yeah," said the sky blue pegasus. "I thought it would be fun, at least for one night." She grinned a semi-maniacal smile, and flicked her tail. Twilight considered the idea for a moment before sighing. "Fine."
"It's gonna be awesome!" said Rainbow enthusiastically, gesturing to the package she had bought earlier. It was a type of ring designed for unicorns to wear. It changed their horn into a cock-like shape. Most unicorns had never had horn sex before, since horns were almost always sharp and could be painful. This small ring fixed that issue however, and allowed female partners to pleasure each other without the use of "toys".
"Only Rainbow could find this..." Twilight muttered, sitting down on the bed to inspect the object. Taking it out of the packaging with her magic, she carefully noticed the intricate details, such as the small carvings and arcane circles on it. "How much did this cost?!"
"Eh, maybe a fifty bits or so? I dunno," shrugged Rainbow. "It'll be worth it, just see." Twilight rolled her eyes and glared accusingly at her marefriend.
"So are we gonna have sex or what?" she said impatiently, imitating Rainbow's voice while suppressing a giggle. The alicorn stretched her wings out, flushing slightly in arousal. She slid off her t-shirt that she had been using, but the blue pegasus stopped her. Instead, she slowly pulled off Twilight's shirt, kissing any bare skin that was exposed. This only made Twilight redden even more, and she began to take off Rainbow's tank top. When both of their shirts were off and discarded, they moved on to the bottoms. The alicorn's skirt was short and tight, her lavender thighs and butt demanding to be freed. Rather than carefully taking them off, Rainbow split the sides open, opting for the quick method.
The blue pegasus let out a moan of desire and her workout shorts were pulled off by Twilight, who was taking her precious time, much to Rainbow's chagrin.
"Come on, Twi..." she whined. "Don't make me wait!" Giggling, Twilight took off her marefriend's panties, and breathed on her clit, her moist warm air tickling Rainbow's marehood. The purple alicorn's lacy, exposing lingerie came off easily as Rainbow undid her sports bra.
"The ring?" Twilight rushed to put it on. As soon as the gold coloured hoop was on her horn, she could feel a warm, tingling sensation in her horn. It surged with magical power, lengthening and expanding.
Rainbow laughed. "Twi, your head is more well-endowed than some of the stallions I know!" Her slit was already beginning to drip with arousal, her legs spread apart to allow Twilight access to her flower.
"Foreplay?" asked the alicorn. In response, a quick nod. She lowered her head, smelling the pegasus' musk. Her scent was intoxicating, filling Twilight with an insatiable lust. She licked Rainbow's clit, sticking three fingers in her marehood. She slid her tongue in as well, her other hand now focusing on the pegasus' clit. Both the mare's wings were sticking out, a sure sign of arousal. Rainbow let out a long, low moan as Twilight flicked her tongue around inside her, brushing her coated walls and making her gasp in need.
"T-Twi, come o-Ahhhh- on.." Rainbow whimpered, impatient. Her breeding instincts were taking over, demanding her to be bred. "P-Put it- ahhhNNnng- in al-already!" Twilight obliged, pulling out her fingers and tongue. She licked the arousal on her fingers, not letting any go to waste. Slowly, she lowered her horn-turned-stallionhood to Rainbow's dripping slit. She pushed her horn in Rainbow, the flared tip sliding in with minimal difficulty. Up until the medial ring, her dick slid in smoothly. When they reached the ring, Twilight pulled out slightly, then thrust back in as hard as she could.
"AhhhhhhHHHh.." Rainbow moaned. Twilight panted along with her, the magically created nerves in her new cock sending so many signals to her brain that she couldn't take it. With a scream, her own marehood became drenched in juices, her orgasm crashing like a wave. She could feel her horn also reacting, swelling with the extra sexual energy. It pushed slightly at Rainbow's walls, but not enough to cause a bulge.
"T-Twi, I h-have an idea-ahhhnn.." Rainbow said. "Make yo-yourself s-some balls.." In between moans, she laughed a bit at the thought, Twilight walking around, a fully erect member on her head, spewing precum. It was funny, but also, very delicious. She licked her lips at the thought of how much fun that would be.
Twilight heard the idea, and obeyed. With a quick spell, two large balls appeared on her head, and her stallionhood began leaking pre, still inside Rainbow. She began thrusting again, aware now that she was closing in on an orgasm once more.
"I'm gonna-!" yelled Rainbow, and her fluids came rushing onto Twilight's forehead. Her cock expanded even more, the juices soaking into the ring. Now there was a slight bulge in Rainbow's stomach, but she was so lost in shear ecstasy that she did not care. She felt the pistoning begin again, and waited. Despite coming out as lesbian and dating Twilight, she had gone out with a few guys before. She waited for the storm of white, hot, sticky seed to come rushing into her waiting womb, the thought bringing her to the edge of orgasm again. The tightness... she needed to feel Twilight cum inside of her, she needed to be bred, to feel her foals kicking inside her. With a yell, she orgasmed again, the member in her pussy engorging itself once more. Though Twilight didn't realize it, her balls had enlarged too, the seed inside churning as she came closer to release.
The moaning mares continued for a single minute more, before Twilight screamed, "I'M CUMMING!" at the top of her lungs. Her balls churned out at least a gallon of seed, the cum sloshing around Rainbow's belly pushing her skin out more and more as her womb grew to accommodate all of it. The ring's power suddenly ended, Twilight pulled her now normal horn out, before panting "That was--"
"Fucking AWESOME!" Rainbow finished for her. They both grinned, still covered in fluids. "Hey, Twi, whaddaya say we take a shower and... clean up?" Her naughty grin tempted the alicorn into accepting. Rainbow sat up, her cum-filled womb sloshing. Some of it dripped out, and Twilight summoned a kind of plug to keep it from escaping. They got up off the soaked bed and made their way into the bathroom, kissing as they did so. Twilight squeezed Rainbow's rather luscious butt, feeling the softness of her matted fur and skin. Rainbow brought her hands up to Twilight's ample bust, teasing the nipples a bit before wrapping her hands around them and massaging ever so gently. The two turned on the water, and feeling the warmth of the water and each other, hopped in, still miraculously locked in a tender, yet very naughty, embrace. Rainbow's tongue slithered into her marefriend's mouth, entwining itself like a serpent around her partner's. Twilight kissed with a newfound ferocity, pushing the soaked pair against the wall and grasping at any and all exposed skin. The two stood there for a moment, then separated and cleaned up.
"I'm- I'm- WHAT?!" The pegasus mare's voice echoed throughout the hospital.
The doctor gave an exasperated sigh. "I said, Ms. Dash, that you're pregnant. Congratulations!" In Rainbow's eyes, little tears were forming, as they were in her partner's.
"Dash--" Twilight whispered. Rainbow stopped her, pushing her lips against Twilight's before she could say anything else. "Dash, I love you."