Zipp Storm paced back and forth in her sister's bedroom, her heart hammering with excitement. It felt a little weird, walking with a length of rubber strapped to her hips so it swung between her hind legs, but she supposed it wasn't any different to what a stallion felt when he had an erection.

She mounted her forehooves on Pipp's bed and practiced a humping motion again, thrusting her hips forward a few times. The rubber cock hung low, and the thrusts sent the end glancing off the side of the bed. The impact carried back through the straps and into Zipp's pelvis, making her giggle.

Oh, how she couldn't wait to show her sister. They were oftentimes emotionally distant, what with their different interests and priorities, and she was hoping a little physical intimacy might bring them closer together on an emotional level, too.

Just then, the door opened to reveal Pipp. She became flustered and confused as soon as her eyes landed on Zipp. "Oh my—" she stammered, her eyes fixed on Zipp's temporary appendage. "Where did you even get that, Zipp?"

"At the sex shop, duh!" Zipp was quick to reply. "Turns out, being a princess gets you toys like this, even if you're underage." Zipp punctuated that by shaking her hips. The flared end of the long dildo bobbed from side to side, drawing Pipp's gaze.

Pipp looked between her sister's face and the strap-on hanging under her barrel, an anxious expression crossing her face. Zipp sensed the worry. "We hardly ever see each other, Pipp. I just… I wanted to share a little time, you know? Draw closer together as sisters." Pipp still looked unconvinced. "Listen, we'll take it slow, alright? It'll be fun. I promise!"

"But I don't want to lose my virginity to that… that thing!"

"Relax—it's not a real penis. You won't technically lose your virginity, right?"

Pipp sighed. "I mean… I guess not."

"Then whaddaya say? You wanna try it out with me?"

Pipp thought for another moment before finally giving a slight nod. "O-ok."

"Great!" Zipp was positively glowing, the grin on her face stretching from ear to ear. "So, uh, you wanna just lay yourself on the bed there?"

Pipp positioned herself accordingly (and somewhat instinctually), laying her front half on her bed with her forelegs tucked under her and her hind legs braced against the floor. Zipp came forward and easily mounted Pipp with her greater height.

Zipp's cock ran up under Pipp's barrel until it hit the bed. Pipp gasped as Zipp pulled her hips back, allowing the hoof-thick tip to slide back out from under Pipp. Soon, it was squarely aimed at Pipp's marehood.

Zipp touched the tip of the strap-on to Pipp's lower lips. She bent forward and brought her mouth up close to Pipp's ear. "You ready for this?" she whispered.

Pipp nodded slowly, biting her lip.

With a shift of her hips, Zipp began to push forward, mashing the tip of her fake cock against her sister's folds. The shaft began to bend, but Zipp kept the pressure on, pushing herself forward as Pipp's nether lips began to spread for the intruder. Her sister was grimacing, likely from the stretching sensation, and, for a moment, Zipp wondered whether the dildo would fit into Pipp after all. However, her worries were laid to rest when the flared tip finally shot past her sister's entrance, the intense pressure she'd been putting on the strap-on forcing it through her labia and into her vagina.

Pipp cried out as the dildo ruptured her hymen and bulled her virginal walls apart. The only thing stopping Zipp's first thrust from carrying the dildo all the way through to her cervix was the sheer tightness of her sister's pussy as it clenched around the rubber of the fake cock she was burying inside her. Pipp was never going to fit the dildo's full 18 inches inside herself, but Zipp was certainly going to have fun helping her try.

Zipp settled her full weight on her sister's back and began to pull her hips back for a second thrust. Pipp let loose a long moan as the edge of the dildo's hoof-wide flare dragged backward along her walls until it was almost stretching out her labia again.

"Here it comes again!" Zipp declared. Pipp raised her head and gave an animalistic groan as Zipp shoved her hips forward. The rubber length surged into her canal again, getting even further than before. The dildo's medial ring was now only a couple inches outside of Pipp's now-winking pussy. It had begun responding to the dildo's presence, secreting juices to help it glide through her better. When Zipp pulled out again, the rubber length was glistening with Pipp's pussy juice. "See? I knew this'd be fun for us!"

"Y—h-haah, y-yeah," Pipp managed to get out without looking back as Zipp pulled out for a third thrust. This time, Zipp pushed back in sooner and pulled out almost immediately. Gradually, she worked herself into a rhythm, rutting her sister with long strokes of her rubber cock, her athletic hips more than enough to counteract Pipp's tightness.

With each thrust, the dildo's medial ring got closer to Pipp's pussylips and the head got closer to her cervix. As Zipp delved deeper into her sister, Pipp's moans and gasps got louder, the head of the cock rubbing over her G-spot with every stroke.

Zipp was in absolute heaven. Even though she was receiving absolutely no physical pleasure whatsoever, she could feel her bond with her sister strengthen each time she thrust into her pussy. The only time she'd felt more proud was when she'd gotten a chemistry set for her birthday and set off an explosion in the castle kitchens.

Pipp yelped as the medial ring bumped into her pussy lips. Zipp had managed to get 12 inches of cock into her sister so far, but she could feel more space inside her to stuff. She switched from thrusting to grinding, maneuvering her hips around while pushing forward in an attempt to push the thick ring inside.

"Z-Zipp!" Pipp cried out. "Puh-hnnguh, pleeease stooop!"

Zipp froze. "What's wrong?"

"I… I don't want this," Pipp whimpered, tears appearing in her eyes. "G-get that th-thing out of m-me."

Zipp drew back, her mind racing. "You didn't want this?" she asked, fearing the worst. "What do you mean 'this'?"

Pipp squeaked and buried her face in her hooves as the flared end of the dildo passed through her lower lips. "You p-putting it ins-side me." She was openly weeping now. "I… I was waiting for the right colt." She looked back at Zipp, her tear-streaked face sending a pang through Zipp's heart. "You know I love you. I'm your sister! Why didn't y-you just say you wanted to be—" Pipp let loose a sob. "C-c-closer?" She buried her face back in her hooves and folded her ears back.

"I'm so sorry, Pipp," Zipp said, a tear trickling down her own face as she realized what she'd done, and how little what she was saying could mean in that moment. "I… I did want to be closer, but I just… I didn't know how to ask!" I just raped my own sister, she thought, looking down at the glistening rubber length she'd been forcing into Pipp not a minute ago. Buck me, I just raped my own sister! She'd never felt so disgusted with herself, or so completely evil. The signs of hesitance, the protests, the grimacing as Zipp had forced her way in, they were only now registering with her. "I… I'm sorry," she said again, unsure what else to say.

"Just… just go away," Pipp sobbed, her voice muffled with her face buried in the bedcovers. "Go away and l-leave me alone."

Zipp ran from the room, the rubber cock still swinging between her legs and dripping a trail of Pipp's juices to the floor.

Zipp was wracked with guilt over the next days. She tried not to let it show, especially in front of her mother, but she couldn't help but hang her head slightly, especially when Pipp was around. She couldn't sleep, and the bags under her eyes were clearly visible against her white coat.

As for Pipp, she didn't say a word. The sisters were farther apart than ever before, and Zipp knew it was all her fault. She knew there was nothing she could say that would fix what she'd done to her sister. She could only hope Pipp would forgive her, even if there could be no forgetting.

Author's Note

Please don't hesitate to leave a comment, and, if you want me to write more stories like this, message me on Discord at Arkadios#8775!