Synopsis: During the hottest days of the summer, everyone in Gravity Falls is trying to find ways to keep cool: from going to the community pool to buying their weight's worth in ice cream sandwiches, everybody was finding a way. Dipper and Mabel decide shedding most of their clothes and sitting in front of an electric fan in their room is the most convenient (and lazy) way to stay cool today. However, Dipper's budding pubescence becomes a bit of a problem for the twins. It looks like Mabel will have to give her brother a hand so he can keep his cool. Rated M, for Mabel. Pinecest, Oneshot.

Author's Note: It's been ages since I actually put words down on a page for a story, so my formatting may be atrocious. I kinda of wrote this story on a whim without any real premeditated thought or structure to go on, but I like to think it turned out alright.

Summer Heat

Heat. It was a powerful force of nature. The all but blazing inferno that was Gravity Falls had become a sweltering atmosphere of misery and sweat. How could anything survive such an intense climate? Local twins Dipper and Mabel Pines, awoken early this morning by the sudden heat of the rising sun, were just becoming conscious enough to ponder this exact problem.

"Eerreuuuugghh," groaned Mabel as she became aware of the intense heat surrounding her on all sides. She, like Dipper, had slept above her sheets and blankets. Mabel rubbed the sleep from her eyes and sat up in bed. "It's even hotter than yesterday," she complained to no one in particular. Her hair was a frizzy mess, partly from the sleep, but it had clearly been exacerbated by the intense heat.

Dipper had also awoken with an unpleasant groan. Mabel certainly had been speaking the truth. Forcing his eyes open, he looked down to see – yep, morning wood. Dipper's eyes widened as he noticed the bulge sticking up from his boxers; normally his sheets and blankets would make this condition much less noticeable, but that was not the case today. "Oh geez," Dipper thought to himself, not wanting Mabel to see. That would start the day off on a pretty weird note; best to avoid that. After quickly glancing over at Mabel to ensure she hadn't looked over and noticed his condition, Dipper turned his body to face the wall. He breathed a sigh of relief; Mabel hadn't seen anything. This was not an uncommon ritual for Dipper; many days now he'd wake up and find himself unable to leave bed immediately, lest he unabashedly inform his sister of his budding manhood. "Now to just wait a bit for it to go dow—," Dipper would've finished the thought, but was interrupted by his dear sister Mabel suddenly surprising him with a womp to the face, transferred via pillow from across the room.

"WHOMP!" shouted Mabel, proud of her hawk-eye shot, "C'mon Dippingsauce, we've gotta find a way to beat this heat before we melt!" Her words carried less energy than what would be considered standard of Mabel; this summer heat was clearly taking its toll. Mabel leapt from her bed and began dressing herself for the day. Dipper, still preoccupied with dispatching with his morning wood, replied shakily, "Yyeah," Acknowledging her brother's agreement, Mabel shed her night gown and brought a clean shirt, in lieu of her normal sweater attire, over her head. Donning skirt to match the shirt, Mabel bolted to the door of their shared bedroom. "Meet'cha downstairs for some breakfast, pronto, bro-bro!" Mabel yelled as she began her journey downstairs to fetch some breakfast. It was definitely a morning for a cold breakfast like cereal. "Hoo…," sighed a relieved Dipper sighed as he rolled upright and out of bed, his erection still jutting out from him beneath his boxers.

Some short minutes later, Dipper entered the kitchen sporting his trademark shorts and t-shirt, although lacking his trademark vest and hat; it was much too hot for those today. Both of the twins gathered a bowl and spoon for their breakfast; both looked forward to the cold milk. "As the twins began devouring their respective breakfasts, consisting of "Sergeant Sugar" and "Choco-O's" cereal, Mabel continued the conversation they'd left off in the bedroom. "So, I am totally not in favor of going back to the pool again today; trying to squeeze in along with the other ten thousand people was a nightmare yesterday!" Mabel exclaimed. "Agreed. I never want to be that close to Old Man McGucket again," Dipper replied with a grimace. Mabel nodded in agreement, 'So, what's a good alternate plan? This heat is already unbearable and it's still early in the morning!" "Well, going anywhere cool or going to buy anything cool would require going outside, which would be a nightmare, so I vote we just stay here and find a way to keep cool," Dipper replied between bites of chocolatey cereal. A cursory glance around the room granted him no real inspiration as to how to keep cool today. There was the fridge, but he didn't think he could survive all day stuffed in there. There were a few ice pops in the freezer, but Mabel and Dipper had realized over the last few days that those were best saved for the hottest times of the day around noon. Mabel also had begun looking around the room, but yielded the same results. Although being stuffed in the fridge all day looked to be a much more viable idea through Mabel's eyes.

Dipper's mind, digging through observations and memories in an attempt to make a breakthrough on their brainstorming, suddenly recalled something of note. Hadn't he seen a fairly large electric fan stored in the attic's closet? Dipper's eyes perked up as he was now sure that he'd seen it earlier in the summer when he'd been putting some of his things in said closet. "Ah! I think there might be an electric fan in the closet upstairs! It was there when we moved our things in at the start of the summer. Let's go fish it out!" Dipper exclaimed, excited that relief from the heat may have been found so early in the day. Dipper and Mabel chomped and gulped down what remained of their breakfasts and bolted upstairs.

Perhaps bolting up the stairs was not the best idea. Dipper and Mabel now stood, both drenched in sweat, at the doorway to their shared attic bedroom. As Dipper entered the bedroom, he decided to go ahead and dismiss with his shirt. It was too damn hot for shirts today. Dipper felt sorry for Mabel for being less able to enjoy the freedom of going shirtless due to societal restrictions. With any luck, the electric fan would keep them cool enough that his shirtless advantage wouldn't bother Mabel. Little did Dipper know that these societal restrictions were of no consequence to Mabel; she'd have chucked her shirt just as quickly if she hadn't been more focused on finding the fan at the time. After all, it was just the two of them hanging out up there.

Dipper opened the closet door and shoved some clothes off to the side, revealing an old, albeit large, electric fan. Dipper and Mabel exchanged excited glances as they both took a side of the fan and lifted it out of the closet. The twins promptly set the fan up in the middle of the room and plugged it in. After plugging it in, the two sat eagerly in front of the fan, both hoping it would work. Dipper reached to turn the knob on top of the fan. He turned it on its lowest setting first, to be safe. The blades began turning, quickly reaching a good speed as the fan began flowing air at a nice pace. The air wasn't cool, but it was extremely relieving compared to the stagnant, still air that was plaguing the room before. "Aaaahh," sighed the twins in unison as the air began to blow over them, giving a cool sensation due to their sweat. "Dip, I think this is the best idea you've ever had," Mabel said as she began pulling her shirt up over her head. It was still too damn hot for shirts today. Dipper's eyes, however, were closed at the time, enjoying the breeze the fan was giving him. He did, however, hear the faint fwip of what sounded like an article of clothing being tossed across the room. Dipper turned his head to where he thought it had landed, and opened his eyes. Surely enough, he saw Mabel's shirt now lying across the room on the floor. "Uh oh," thought Dipper as he realized what that meant.

It certainly wasn't a foreign idea to Dipper that his sister was cute. She enjoyed reminding people, Dipper included, of this fact on a regular basis. In addition to her cute appearance, Dipper was also aware that he enjoyed her personality. He'd be lying if he said he didn't find her unabashed demeanor…appealing. He'd pondered to himself before whether or not these observations of his sister were just simple, empirical enjoyment of a close friend (and sister's) features, or if they meant he was admiring her because she possessed all these aspects that he found attractive.

Another undeniable fact was that Dipper's body was in a perpetual state of craving procreation. Puberty was not being kind to the poor boy, as he was frequently forced to slouch and find ways to exit rooms surreptitiously to avoid alerting everyone of his sudden, inexplicable erection. His body was constantly reminding him of every attractive feature attached to any female in sight. And, as ashamed as he was to admit it, Mabel was no exception. Whether he wanted to or not, his body was going to make him notice every curve of her body and every perfect curl of her hair.

Despite her easygoing appearance, Mabel wasn't exactly strutting through puberty with ease, either. It was obvious she was in her "boy crazy" phase since the beginning of the summer, but, since then, more physical changes had begun taking place. She'd gotten taller, much to Dipper's chagrin, and her breasts had begun budding quite nicely, not to Dipper's chagrin, as the weeks had passed. She'd also felt the biological imperative to procreate on many an occasion since the summer had begun. Luckily for her, her body's messages to procreate didn't create the awkward effect like a sudden erection would. That said, she was entirely comfortable being around Dipper during this odd phase in her life; she knew that if there was one person who she could trust and confide in, it was Dipper, so there was no need to be shy or embarrassed around him. The same could be said of Dipper; he didn't have to be as shy around Mabel regarding these odd changes they were both going through, but his natural demeanor wanted to downplay anything weird. Looks like Dipper may have to step up his game to downplay the current scenario.

"Aaaahh….," Dipper could hear Mabel sigh in relief as the air passed over her now-naked torso. Dipper fought hard to not immediately turn and look at the pretty sight that sat beside him. Dipper couldn't say he was that surprised at Mabel's carefree discarding of her shirt; they were very close, after all. And if there were ever a time where getting as naked as possible were appropriate, this seemed to be it. Dipper paused, taking a short breath before turning back to face the fan, allowing the breeze to blow over his face once again. He fought hard to not let his eyes dart toward his peripheral vision on his right and just outright ogle his sister. "This was the best idea, Dippingsauce," praised Mabel, unaware of her brother's growing plight. She looked over to see if Dipper was enjoying the effects of the fan as much as she was, only to see a fairly rigid, stiff Dipper staring straight forward, blinking on occasion due to the moving airflow over his eyes. "Haha, yeah," Dipper replied, failing miserably at sounding nonchalant. He attempted to look less stiff by moving his eyes about the room, but he could only bring himself to look in directions toward his left, away from Mabel. "Dip? Something wrong?" Mabel asked with honest eyes. Before Dipper could respond, Mabel was suddenly struck fiercely by an all-too-recent memory.

During her time in Dipper's body due to the effects of the "Electron Carpet", Grunkle Stan had imparted on her some…interesting knowledge. Most of this knowledge was specifically for Dipper. Mr. Pituitary and his big plans and all that. Mabel remembered the descriptions and diagrams given to her by the book, and, unfortunately, Grunkle Stan's bombastic narrations. She quickly remembered the bodily changes the book described and the physical reactions boys' bodies have to certain stimuli and all. Surely enough, she arrived at the realization that she may've been making Dipper uncomfortable with her shirtlessness. She also arrived at the realization that the best thing to do was probably tease him about it.

"Ah-haaa," Mabel knowingly chimed as a big, silly grin spread across her cheeks. Dipper still sat stock still, looking forward, and moderately confused. Mabel patted him on the shoulder compassionately, "I understand! It's hard not to be all riled up over all this!" Mabel gloated as she gestured toward her developing body. Dipper still didn't look, but was taken aback by Mabel's sudden display of playful narcissism at his expense. "Darn it. She figured me out, and now she's going to tease me about it forever. Though I suppose I should be thankful she doesn't seem grossed out, at least," Dipper thought. It was true; Mabel wasn't grossed out at all by her brother's shameless admiration of her body. Mabel had, as Dipper had, always felt there was a particular closeness between them that was beyond what normal siblings, or even normal twins, had.

"Mabel, uh—I—," Dipper tried to begin explaining/apologizing, but was stopped in his tracks by a sudden hug from his sister. "No worries, Dip. I know what you're going through," Mabel interrupted. "You do?" Dipper replied, a bit skeptical. Mabel had never outright told him that Grunkle Stan had given her "the talk" while she was in Dipper's body. "Mmhmm," Mabel responded without pause; she let the hug dissipate and returned to her seated position next to Dipper. "Remember when we switched bodies because of that carpet thing? Grunkle Stan forced me to listen to "the talk" while I was still in your body. So…yeah, I guess I kinda have a good idea of what you're going through right now, and it sounds rough, so don't worry about it!" Mabel continued. Clarity washed over Dipper's face as he realized exactly what that explanation entailed. His face flushed a bright red as he thought about the fact that Mabel knew exactly what was going on with his body while he was trying not to ogle her. He also felt somewhat embarrassed at being somewhat ignorant of these changes and what all they meant. Since Mabel had received "the talk" from Grunkle Stan, Dipper had been left to figure out the vast majority of the subject on his own. He wasn't slow, but he was having trouble tumbling through the opening stages of puberty with any measurable amount of grace. Luckily, Mabel was good at making Dipper feel like he didn't need to ever be graceful. She liked him just the way he was: sweaty and awkward.

Having returned to their original, seated states, the room fell quiet for a moment as the twins went back to enjoying the fan's cooling effects. Dipper, despite being put at ease by Mabel's kind words, couldn't help but notice "Little Dipper" attempting to put itself on display for all to see. "Oh come on. Just go down already," Dipper tried to command his lower appendage, but to no avail. His shorts were becoming much tighter as his erection became full-blown. Dipper shifted his sitting position to try to hide it, but there was just no way to hide it this time. Dipper's cheeks flushed a bright red once again and he put a hand over his face in a gesture that showed he'd given up trying to hide it. Mabel's attention was drawn to Dipper by his sudden exasperated gesture; her eyes looked him up and down to see what was wrong. "Oh,"Mabel thought as her eyes made contact with the bulge in Dipper's shorts. "It's that thing where the thing does the thing," Mabel's mind recalled the diagrams in the book. Surprisingly enough, even Mabel's cheeks began to blush a bright red. Although it was a little weird, she was frankly flattered that Dipper found her so attractive.

"Oh, ha-ha, is uh, 'Little Dipper' trying to butt in?" Mabel teased, pointing at the bulge. Dipper's facial expression was a difficult one to read. This was mainly because he was very unsure of how exactly he felt about his sister commenting on his indiscriminate erection. He was also very unsure of whether or not he was okay with said erection being personified as "Little Dipper". But these were thoughts for another time; his current predicament was becoming a bit painful. His erection strained against his boxer briefs and shorts, pulsing rhythmically.

Had Dipper been able to look at Mabel, he'd see that her eyes were fixated on the rhythmic pulsing at the front of his shorts; it was an odd sight to behold for a twelve-year-old girl. Mabel's heart rate was elevated; she was becoming somewhat excited over the events occurring in front of her. Dipper, obviously already excited, was about to give in to the urge to turn his body away from Mabel and excuse himself. Something stopped Dipper from turning, though. "Boop," narrated Mabel as her finger poked the tip of Dipper's erection. Dipper's facial expression was one of flabbergast. He winced as the sensitive tip of his erection was prodded by Mabel's index finger. "Aah, quit it, Mabel!" Dipper asked through shut eyes, his voice crackling as he did.

"Nuh uh," denied Mabel, poking the tip again. "Bop." This time, Dipper tried to twitch his body back, away from Mabel's fingertip, but her fingertip followed. The stimulus had caused Dipper's boyhood to begin leaking pre-cum. There was no visible sign of it yet, but it began to stain his boxer-briefs. Mabel's cheeks were bright red from the reaction she was getting out of her brother; he was so sensitive here! "C-c'mon Mabel, cut it out," Dipper stuttered. "Aw c'mon, Dip. You didn't get the proper lesson on this kinda thing like I did; I'd be more than happy to get you up to speed," Mabel responded with sincerity. Dipper's eyes darted up, then down, then over to Mabel. "Well…I guess that makes sense," Dipper responds, locking eyes with his twin. Mabel met Dipper's gaze with an empathetic and comforting one.

"Of course it does, Dippingsauce, let's get these shorts off, then!" Mabel exclaimed, pointing at Dipper's shorts. "Already?" Dipper responded, his voice crackling again. His eyes darted down to the bulge in his shorts, then up to Mabel. "No need to be embarrassed, broseph. It's not like I haven't seen it before," Mabel assured. "Well, that's true. I mean we do share an occasional shower whenever we're in a rush. It's just never been… weird… before," Dipper reasoned to himself. Dipper took a breath and reached down to unbutton and unzip his shorts. He slid the shorts down to his knees and kicked them off, landing them next to the fan.

He had to admit that the cooling breeze of the fan was much more drastic when his shorts weren't covering up his legs. However, his relief was short-lived as Mabel eyed his boxer-briefs expectantly, silently telling him to remove them. Dipper understood that there wasn't much point beating around the bush with Mabel, so he took the elastic strap of his boxer-briefs in his hands and began to tug them down. As he pulled them down, his erection posed an obstacle, jutting out further forward as the material tugged against it. Mabel watched on with curious eyes, despite her earlier declaration that she was just going to get Dipper "up to speed". Dipper pulled the elastic band outward, giving his erection room to breathe as he finished pulling his boxer-briefs down to expose "Little Dipper".

It was fully erect and throbbing. Dipper's foreskin hadn't pulled back much, though; being fairly early into the stages of puberty, his girth was a modest one. Dipper's cheeks had seemingly become permanently flushed at this point. Dipper's eyes darted back and forth as he waited for Mabel to say something; hopefully that something would be helpful and enlightening.

"Ha, weird," Mabel observed. Dipper would've been lying had he said he expected any form of tact from Mabel. "Yeah well, I've been trying to keep it under control," Dipper said, trying to get Mabel back on track. Mabel finally took her eyes away from Dipper's hardness and looked up at him. "Oh, well, if what Grunkle Stan told me is true, it's not really in your control, for the most part. It just kinda happens when you start looking at something pretty, or thinking about something pretty. He said it's the body's way of saying you should 'mate' with someone," she explained. "Mate…right," Dipper repeated thoughtfully. He knew some vague details about "mating", or "sex" as it was more commonly referred to, but didn't honestly know any of the specifics. He just knew his body was shouting at him to do something and he wasn't particularly sure of all the specifics of how to go about doing it. It was really aggravating.

Mabel could see Dipper's expression meant he wasn't entirely sure what she was talking about. "Y'know, sex. Makin' babies and junk. When two people get together and get naked and all," Mabel explained, oddly trying to tip-toe around some of the more grotesque vocabulary words Grunkle Stan had inadvertently taught her. Despite her relaxed demeanor, Mabel wasn't exactly as unaffected by the current scenario as she seemed. I guess you could say even she was a bit uneasy, given the circumstances. Mabel had nothing but love for her little bro, but the situation they were in had them closer than they'd ever been before. Despite Mabel's attempt at describing sex, Dipper still looked at her with a mostly blank expression. "Right, sex. That's how I get…this to go away…" Dipper thought aloud, as he looked down at his erection. "Well, yes and no," Mabel replied, "There's also 'masturbation'."

Dipper's face went absolutely blank at this statement; he had no idea what she was talking about. "Grunkle Stan said that, since this," Mabel said, gesturing downward at Dipper's throbbing erection, "happens so often, a boy can make it go down himself by 'masturbating'. It's kinda like you make-believe you're having sex, and that makes it go down." Dipper was nearly at a point of desperation by now; his throbbing member was leaking pre-cum at a considerable rate, longing for release. It didn't help that what he was imagining due to Mabel's explanation wasn't exactly coherent. "Uhm," Dipper half-sighed, trying to communicate that he wasn't entirely understanding her meaning. "Here, like this," Mabel said, as she, without warning, grabbed a hold of Dipper's erection.

Dipper's eyes immediately grew to the size of saucers; the feeling of someone touching his penis was intense. "Aaagh!" he grunted as his sister's hand gripped him. Mabel looked up at Dipper while she gripped his erection, "Sorry, too rough?" she asked, wondering if she'd hurt him. "Not exactly… just very weird feeling," Dipper responded, not entirely able to find the words he needed to describe the sensation. It wasn't unpleasant; it was difficult to describe. Before Dipper could protest, Mabel began slowly sliding her grip up and down Dipper's shaft, as had been shown in Grunkle Stan's informational picture book. This new sensation rocked Dipper to his core. Dipper moaned and tried to pull his body away, unsure of how to react to the new sensation. Mabel's hand lost her grip as Dipper pulled away. "Sorry, did it hurt?" Mabel asked with concern, looking up at Dipper. "N-no, it just felt…intense. I guess it's…really sensitive down there," Dipper tried to explain to the best of his ability. Mabel nodded, acknowledging that she should be gentler with Dipper's privates.

She reunited her hand with his throbbing member, this time with a gentler touch. Dipper winced, but didn't pull away this time. She lightly began the same stroking motion she had before, up and down his shaft. Dipper moaned again, this time being more prepared for the intense feeling traveling through his penis up through his body. This time he enjoyed the sensation, "Aahh," he moaned at the feeling, overcome with the intense feeling her hand was giving him. Her motions were relentless, stroking back and forth and back and forth over and over without rest; Dipper wasn't sure what it was, but something was coming. He could feel a proverbial climax on its way, but he had no idea how to explain what it was with words. Unable to relay this information to Mabel verbally, his body decided to do it for him."Aah!" he moaned at the height of his pleasure. Suddenly, a hot, gooey spurt of cum shot from Dipper's penis shot forward, landing onto Mabel's unsuspecting face. And, before she could pull her head away, another quick spurt came, striking her on the cheek. Dipper's body had become rigid as the intense feeling of his first orgasm gripped him.

Mabel moved her face out of the way of Dipper's ejaculation, not wanting any more of Dipper's cum to land on her face. "Woah, you okay Dip?" Mabel asked with concern. She could see he was having quite a hard time talking and thinking at the moment. Her hand was now sticky with cum that had finally finished spurting from Dipper's member. She gave his shaft one final stroke as she pulled her hand away, examining the viscous fluid covering it.

Dipper was out of breath. The intensity of the orgasm had taken a heavy toll on the boy. Dipper held up a finger to Mabel, indicating he needed a minute to recuperate so he could talk. He spent the next several moments looking down at his deflating penis and his sister's cum-covered hand and moderately cum-splattered face. The picture before him had gotten him really flustered again, despite having lost his erection due to the orgasm. "Y-yeah. I think I'm okay. Just kinda…reeling, I guess. That felt…it's hard to describe, but it was great, Mabel," he said with gratitude. Mabel could see that he was truly grateful for the crash course she'd just given him; these rough, pubescent days should hopefully be much more manageable with this knowledge under his proverbial belt. "Sorry for getting…stuff…on you. I didn't realize that was gonna happen. What is this stuff?" Dipper apologized. "The book said it's called 'semen', and that it's what's used to make babies when you have sex," Mabel explained, wiping a bit of cum off of her cheek. It was kinda gross, but she knew Dipper couldn't help it; she'd just wipe it off with a tissue when they were done with their "lesson".

"I see," Dipper responded, still somewhat short of breath. He tried to stand, wanting to find a tissue to clean up his now-flaccid member. His legs were wobbly, but he managed to stand. This put his member right at eye level with Mabel, who was still sitting on the floor. He turned to walk to his nightstand, where a box of tissues could be found. Grabbing a few, he returned, giving some to Mabel, and using the remaining ones to clean cum and pre-cum off himself. After retrieving his boxer-briefs and shorts, he sat back down in front of the fan next to his sister. "Hey uh, thanks a lot for this. I really appreciate it a lot, Mabel," Dipper said, looking over at Mabel. "You don't know how frustrating the past few weeks have been with absolutely nothing to go off of," he continued. "No problem, broseph. Anything to help," Mabel responded, giving Dipper a pat on the shoulder.

A minute or two of silence followed, both twins returning to enjoying the cooling effects of the fan. Despite the awkward events that had just taken place, they both seemed to easily segue back into just what they were doing before. If one didn't know any better, they'd have never suspected that the two siblings had just gotten done having a lesson in masturbation and handjobs. After some time, casual conversation was struck up betwixt the two as they began plotting how they would beat the heat once the hotter hours of the day arrived. It was no mystery that it was going to be a long, long day in Gravity Falls.