# Trusting Your Sibling

By: TheDragonBoy

## Content

“Are you sure about this Mabel?” Dipper asked. Putting aside the moral arguments and the deafening awkwardness, this was still one of the weirdest ideas he had ever heard- and this was after spending weeks in Gravity Falls.

“Yes. Definitely. Absolutely!” she replied. It was clear she was very excited about this, though she also seemed a bit nervous.

Dipper sighed, “Alright,” he said. Mabel squealed but then quickly tried to regain her composure.

Am I really about to go through with this? He asked himself. When his sister had first come to talk to him, this had been the last thing he would have expected her to ask. But she had seemed so exposed when she told him- red with embarrassment but also somehow passionate- he could tell this was something she really wanted to try. She probably couldn’t trust anyone else enough to even ask, and besides this was Mabel, he could trust her, right?

Mabel ran over and grabbed the special flashlight from under her bed. After that whole “who’s taller” thing, they had destroyed the original crystal… but they had also forgotten to un-shrink Soos, so they had to go get another. Afterwards, Dipper had changed his mind and suggested that they actually hold on to it; a size-changing flashlight might come in handy. At the time, Mabel had (somewhat frantically in retrospect) asked if she could keep it- after all, Dipper already got to keep the Journal all to himself. I guess now he knew why she wanted it so badly.

Mabel rushed back to Dipper, flashlight in hand, silently thanking the shooting star she had wished on that he had said yes, and that they had the whole Mystery Shack to themselves when he did. She pointed it at him and looked him in the eyes, giving him the chance for second thoughts, but he just nodded nervously.

She flipped the switch, shining the flashlight’s magical beam on her brother, and he instantly began to shrink. Dipper watched through the light as his sister began to “grow” until she towered over him like a giant. She stopped when he was only a few inches tall.

For a moment they both stood still, preparing themselves for what they planned to do. Knowing what was about to happen, he looked Mabel up and down, almost as if he had never seen her before. He quickly realized that from his new height, he could see clear up her skirt and dimly make out her shadowed underwear from beneath. Under normal circumstances he would have quickly looked away, probably even blushed, but that all seemed pretty pointless now.

Dipper’s eyes were caught by Mabel’s hands as they started to move. He glanced at her face and noticed that she had started blushing herself, and had closed her eyes and turned her face away from him. He looked back down at her hands as they moved toward her waist. Her thumbs slipped past the inner bands of her clothes and she gently pushed them down. Without giving herself time to hesitate, she slid her hands down until her garments fell loosely to the wooden floor.

The resulting puff of air was surprisingly strong at Dipper’s level and stirred up dust which got in his eyes. He blinked a few times, and as his vision cleared he could vaguely make out his sister carefully stepping out of her clothes and pushing them to the side. She then quickly bent her knees and rested her bare rear on the floor, using one arm for support.

By the time Dipper could see normally again, Mabel was sitting in front of him, her knees up to her chest and her arms wrapped around her legs, blocking the rest of her body from view. She still had her eyes closed and her head turned away from him. Her face was burning red and she was clearly tense. For a moment, Dipper thought that she might be the one who backed out of this whole thing, but then his twin took a deep breath and opened her eyes. She turned her head to face her brother and they looked at each other over the mountains of her knees.

“You ready?” Mabel asked with a somewhat forced smile, her voice still showed her excitement, but it was clear her nerves were getting to her. She sounded anxious but unsure, like she was asking for her brother’s comfort rather than his willingness. Despite the strange and taboo territory, Dipper still felt the urge to encourage her.

“I’m ready, Mabel,” he said as steadily as he could. Mabel’s smile widened a bit and she seemed to relax just slightly.

Slowly, Mabel let her arms fall to her sides. She extended one leg, then the other to either side of her brother. For the first time, Dipper had an unobstructed view of his sister’s privates. Not wanting to make this any more awkward than it was, he forced himself to start walking forward. The distance between them was several times his current height, so the gap closed slowly.

This is fine, Dipper tried to rationalize, We’re siblings, we must have seen each other naked before. We used to take baths together, I’m sure I’ve seen Mabel’s… thing before. But in truth they had stopped sharing the bathroom some years ago, and by the time he had learned the… differences between boys and girls, they were well past the years when they would have been unclothed around each other.

So as Dipper approached his sister, his eyes were locked on her crotch. Knowing that he had her permission- her encouragement even- he started taking in every detail. Her outer lips were just barely defined, bulging out slightly where they met to form her slit. Short hairs dotted the surrounding area, lightly covering most of the skin between the bases of her legs, ending abruptly just below her waist. Her smooth legs covered the sides of his view, like fallen tree trunks with her budding womanhood as their canopy where they joined.

Before long, he was right in front of it, just an arm’s reach away. He was so close that he could see her pelvic muscles clench up reflexively as Mabel too realized just how near her brother was. He looked up at his sister. She towered above him, her chest moving in and out as she breathed, heavily and quickly. She was looking straight down at him, her bottom lip in her teeth and a small anxious smile on her face.

Internally, Mabel was starting to go wild. He’s so close! I can feel his breath on my lips! This is actually going to happen! Dipper’s definitely the best brother ever for letting me try this with him! But even with her excitement, on the outside she just sat motionless in anxious anticipation, knowing that any large movement would probably scare her volunteer. She wanted to stay as still as she could, so Dipper would feel as safe as possible.

Though Mabel didn’t speak, Dipper knew what she expected of him, she had told him pretty plainly what she wanted. So he looked back down at his sister’s privates, took a deep breath and slowly reached out his hand.

Mabel shuttered as Dipper made contact with her skin. This was the first time she had been touched by another person, by something that moved completely without her control. Dipper’s hand rested just to the side of her slit, he could feel her body quiver as it adjusted to his presence, feel her pulse as it pounded through her and feel her heat as it radiated from her bare skin.

Alright, here we go, Dipper thought. He slowly applied some pressure to his hand and started to push to the side. The skin began to wrinkle and stretch around his fingers as he slowly spread open one side of his sister’s lips. He could hear Mabel take a deep, shuttering breath, her anticipation enhancing the experience many times over.

Dipper stared in a sort of strange fascination as the peachy skin parted to reveal the deep red interior of his sister’s privates. He had definitely never seen anything like this; even if he had seen his sister naked before, to see her up close like this and at this size…

So this is a vagina, he thought to himself. He stared for a moment longer, until a small trickle of clear fluid started to leak from the tiny opening he had made. That brought him back to his senses. Wow, I guess that means Mabel is really eager.

Not wanting to keep his giant sister waiting, he tentatively reached out his other hand and slipped it wrist-deep into the folds of red flesh. He could feel Mabel’s entire body suddenly clench up as she took a sharp breath, and he felt the edge of her vaginal walls squeeze around his hand. He reflexively pulled back. For the first time, he seemed to realize how much smaller than Mabel he was; how much weaker he was than her at this size. Would this even be safe? Would he be crushed if he really…?

He looked up at his sister. She stared down at him intently, her face clearly showing strain as she tried to contain herself. All traces of nervousness were gone now, they had passed the point of the awkward. Though she still refrained from speaking, knowing that she had no right to urge Dipper to do this, it was clear that inside she was begging for him to get on with it,

Dipper looked back down at his hand, now covered completely in clear fluid from the inside of his sister’s nethers. It’ll be okay, he rationalized, this is Mabel, I can trust her.

Mustering up his determination, Dipper took his hands and wrapped his fingers around the edges of Mabel’s lips. Slowly but surely, he pulled them apart, revealing her entrance almost completely. Again Mabel shuttered, but not quite as much this time. Perhaps she could feel her brother’s reluctance? Or maybe she was already getting used to this level of stimulation? Either way, it gave Dipper a little bit of hope.

Steeling himself, he started to slide one arm in further, parting the red walls and exposing the shadowed tunnel within. There was a noticeable amount of fluid trickling out now, and plenty coating the interior, so he was able to move with almost no resistance. It was as if Mabel’s body was welcoming him inside.

He looked around one more time, and it really started to sink in just how much bigger Mabel’s body was right now, the size of her legs and her chest, of her face up above in the distance; a body plenty big enough for him to disappear inside of.

Dipper took a deep breath, and then pushed. His legs propelled his head and chest into his sister’s folds, his arms still keeping the entrance open. Mabel squealed and every muscle in her body clenched, including the muscle surrounding her brother. Her lips squeezed together, pinning Dipper’s arms to his sides and applying a somewhat uncomfortable amount of pressure to the rest of his body.

“Mabel!” he exclaimed, though he felt so small and hemmed-in that he doubted she could hear him. Whether in response to his words or his actions, he could hear- and indeed feel- his sister speak.

“Dipper, that feels so good!” She let out a long sigh blended with a moan as her body relaxed. Dipper breathed heavily as the pressure on his chest was released, but the air was thick with his sister’s scent- something he had somehow failed to notice until now. Maybe he had just gotten used to it after living with her for so long? Just not at this intensity.

Dipper was definitely rattled now, so he did what he always did to settle his nerves: he thought. On one hand: he was stuck halfway up his sister’s vagina (a place where in all decency he should never be), covered thoroughly in her “other fluids”, without much room to move- maybe not even enough to get out if he wanted to. On the other hand: Mabel really seemed to be enjoying this; if his experience with his own privates and his history with Mabel meant anything, it seemed to him this might be one of the most exhilarating things she’d ever experienced. He thought back to just a few moments ago when Mabel had confessed her desires to him, and imagined her reaction if he chose to back out now. He had known this would be awkward and uncomfortable, maybe even dangerous, but he had come this far.

Taking in as much air as he could, Dipper gave one final push with his arms and legs, lifting his feet off the ground and submerging himself in Mabel’s insides up to his knees.

“Dipper!!” Mabel screamed. She felt her nethers squeeze- harder than she had ever felt before, harder than she thought she could. She reflexively shot a hand down to her crotch, clasping it over her entrance and inadvertently pushing Dipper in the rest of the way.

Mabel couldn’t believe it, she could feel him inside her. He was all the way in, every inch of him from his head to his toes completely encased by her body. Except for her, no one would even be able to tell he was there, he was all hers! He started squirming immediately, but all that did was stimulate her even more. Whether she wanted to or not, she found herself contracting around him rhythmically as he pushed. Her fingers instinctively went to work, rubbing at her walls and her clitoris. She had never felt anything like it. With every pulse, she could feel Dipper’s body distinctly, moving even deeper inwards towards her core.

In the back of her mind she was worried of course, worried about how hard she was squeezing, about how much air was in there for him to breathe, about the startling amount of fluids that seemed to flow out of her in a never-ending stream. But it just felt so good, and a part of her mind told her that it was too late for worries now. He was so deep at this point that she might not even be able to reach him without triggering more contractions and pulling him deeper. His best chance now was for her to finish as quickly and as grandly as possible.

Inside, Dipper was struggling to maintain some semblance of control. Mabel’s heartbeat was a pounding pulse in his ears and each contraction felt like she was sitting on him. He could hear her moaning and breathing as his movements unintentionally spurred her on. At first he had tried pushing himself toward her entrance and calling out her name, but now his body was moving almost instinctually: his arms trying to shield his face from the onslaught of the vaginal muscles and trying to keep the area in front of his mouth clear enough to breathe, meanwhile his legs spasmed almost uncontrollably in protest and his chest started to feel sore as he was hammered and continued to fight to inhale.

He couldn’t feel any of the relatively cool, summer air of the outside, as every bit of him was covered in hot slimy lubricant and pressed ever inward by his sister’s strong, young vagina. As the turmoil continued, he felt Mabel start to shift around as she gave in to the sensations. So in addition to the violent pounding, the direction of gravity started to roll about, and he could add nausea to his list of discomforts.

What was happening? He thought frantically. Was she doing this on purpose? Couldn’t she control herself? Was she going to crush him inside of her? He was starting to lose hope when he heard his sister’s muffled voice, “Dipper! I’m almost there, hang on!” Even in the state she was, she was still concerned for him- at least he hadn’t been forgotten. So Dipper kept fighting with the last of his strength.

“Come on Mabel! I trust you!” he yelled as best he could.

Mabel’s fingers had begun to move at a violent pace, she could feel her walls pulsing faster, faster. Something inside her was building up and Dipper was right in the center of it. Finally, she felt her whole body tense, so sharply that she thought she might injure even herself. She felt her vagina squeeze her brother tightly from the top down, forcing him out of her entrance with a gush of juices. She screamed as the powerful sensation rushed through her. Suddenly, she felt herself empty, and she let herself collapse back on the wooden floor.

Dipper coughed violently as he swatted at the slimy fluid covering his face. His whole body was sore and the light of the room seemed far too bright to his eyes. He was soaked from head to toe and quickly became cold as the heat of his sister’s insides faded.

It took a while, but eventually Dipper felt himself begin to relax, still sprawled out on his back, breathing heavily between his sister’s outstretched legs as she did the same.

“Dipper?” she called breathlessly.

“Yeah?” he responded weakly.

“Thank you.”

Originally Published: 27-May-2018