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When his partnership with his best friend took an unexpected and exciting new path, Hiccup didn't anticipate just how much his relationship with Toothless would flip. He found the tables turned, becoming trainee to his dragon master.
When Hiccup first invited Toothless to mount and fuck him, he broke the ultimate taboo and the walls between the two of them came crashing down. There had been doors he tentatively opened one at a time, but when Hiccup crossed this red line, the barriers disappeared entirely. He stopped feeling guilty and ashamed, and he opened himself to any expression of affection, passion and sexual fulfillment that the two of them could conceive of and agree to explore together.
What began with the dragon's accidental discovery of the delicious treat that his human friend produced naturally, an innocent craving that drove Toothless to obsession initiated a process that guided Hiccup through a series of emotionally agonizing but physically exhilarating steps. First, Hiccup allowed Toothless to eat the semen that the boy spilled by his own hand, satisfying the dragon's hunger. Gradually the boy began to allow his friend's eager tongue to bring him to the release that was their mutual reward. And then when that escalation to a sexual context introduced the dragon's own lust, the boy's sense of fair play eventually required him to apply his hands to bring about his friend's mutual orgasmic conclusion. Further experimentation finally led the boy become curious enough to ask the dragon to mate him, and now there was no holding back.
Hiccup and Toothless fucked every day. Alone at home when Hiccup's father was away. Locked in the supply room at the dragon-training academy. In the coal shed behind Gobber's forge, when Hiccup's boss went home for his lunch break. In the forest, dappled by the shade through the trees. Bathing at the cove where the first friendship between a Viking and a dragon was born. Anywhere, any time they could manage.
Hiccup propped himself on his hands and knees, receiving an injection of dragon cock from behind. Sometimes he laid on his back and raised his legs, wrapping his arms around Toothless while he was pounded into the ground; smearing his face damp with his passionate drool against the dragon's skin, pebbly but so buttery soft, like treated leather. Or Hiccup crouched on top while Toothless reclined, feeding his ravenous asshole with red and oily dragon flesh, settling his hips down slowly and claiming the throbbing cock inch by inch until Hiccup bottomed out.
Toothless was not yet fully grown when he first came into Hiccup's life. Both of them were adolescents. The dragon hadn't reached sexual maturity when their sexual adventures began. A cock that was roughly equivalent in size to Hiccup's own endowment when it was first sheathed in the boy's guts had a ways left to grow. Perhaps triggered by the dragon's introduction to mating, a growth spurt resulted in a cock that nearly tripled in mass. Much of it in length, but also with a significant increase in girth. Hiccup's body was still going through changes, too, but his came at a much slower pace. The transformation of the dragon's penis took only a couple of months, but the pair's appetite for sex provided for Hiccup to be exposed to the difference gradually enough that he adapted safely.
Hiccup's body was trained. Trained to perform a dazzling and wonderful trick. He made a giant cock disappear. What was already very satisfying copulation for the boy got even better. There was some pain, but it was a good pain, an earthy note under the full flavor of overwhelming pleasure. The throb and sting that lingered after a good fuck prolonged Hiccup's satisfaction. It reminded him throughout the day of the ecstasy he and his best friend arrived at together. Ecstasy that they would visit again soon. He was driven wild by being stretched and filled.
And he was filled. Oh, gods, was he filled. By the time Toothless finished developing, Hiccup was no longer able to contain everything the dragon was capable of putting into him. Hic's cup runneth over. The increase in the size of the dragon's organ was dwarfed by the increase in the dragon's semen production. Loads that had already been several times larger than Hiccup's gradually compounded in volume until they literally could not be contained.
When Toothless climaxed, huge jets of cum were released at high pressure. The dragon's hefty cock stretched the walls of Hiccup's tight channel to their limits, but the boy's anal ring still wasn't snug enough to hold back the massive loads of semen that the dragon pumped out. The liquid injection overwhelmed the capacity of Hiccup's winding, velvety chambers. The dragon's cum rebounded and squirted out around the fleshy plug of his flexing cock. Toothless bleated, and Hiccup answered with his own urgent cries as the pressure became too much and cum sprayed his thighs. Thick goo splattered their skin around where their bodies joined. When the dragon's spent penis shriveled and returned into his body, cum flowed out of Hiccup's winking asshole like a tapped barrel and a pool of it slowly spread underneath him.
Though this had all started with the dragon's appetite for the boy's cum, in the beginning Hiccup lacked any curiosity about sampling the dragon's emissions. Before he had invited Toothless to fuck him Hiccup had only used his hands to deliver the dragon's climax, and he offered his slimy fingers to the dragon, who methodically licked up his own mess without any special enjoyment after he savored every drop that was Hiccup's creamy gift.
But for a long time, Hiccup was squeamish about tasting dragon cum, or putting his mouth on his friend's cock. Despite how good it made the boy feel that Toothless relished Hiccup's seed, devouring every drop like it was precious, Hiccup didn't return the interest. The dragon's enthusiasm was somewhat infectious, and that might have tempted Hiccup into oral experimentation earlier, except that the dragon's cock itself was... well, gross. It may have been the greatest thing Hiccup had ever felt in his entire life, but it looked very unappealing. It was red and slippery, with a skinless appearance. Purple veins decorated its surface and it wept an oil that lubricated its passage through Hiccup's fingers or up his backside. The cum itself appeared much like Hiccup's, just somewhat thinner in consistency and with a pinkish tint.
But when the volume of the dragon's seminal output multiplied so drastically, it became inevitable that with the stuff getting all over the place some of it found its way into Hiccup's mouth by chance. And the boy was surprised to find that it tasted quite nice. Good, in fact. Even great. It was very sweet, and sweet was a flavor that Hiccup had always enjoyed very much but it was hard to come by where he lived. He licked his fingers, eating more dragon cum. There was a spicy element to the substance, too. A little bit of a burn. It was similar to cinnamon, another rare commodity on Berk.
Hiccup scraped his hand over his belly, gathering a handful of Toothless's load from where it lay after the splattery finish of their latest fuck session. The boy held his cupped hand to his face and slurped spicy-sweet pink dragon cum from his palm. Toothless watched with stunned fascination, and his wide-eyed and droopy-"eared" expression made Hiccup laugh.
"This is really good, buddy!" Hiccup exclaimed, "I love it!"
The dragon beamed a gummy smile and tackled his friend. Toothless wriggled and panted, wrestling Hiccup as if he were a puppy instead of a great big dragon. Hiccup laughed and played along, pleased to make his best friend so happy.
The pair's sexual repertoire opened up even further. Hiccup tried putting his penis into the dragon's genital slit. Toothless lay on his back, and Hiccup crawled onto his big warm body. Hiccup ground his hips into that blessed spot that issued forth his favorite object in the world from his favorite person in the world, which itself issued his new favorite flavor in the world. When Hiccup got hard he slipped his cock into the slit, finding it oily and hot. And tight, wonderfully tight. Toothless growled at the invasion. Maybe it hurt him a little. But if it did, he bore it for his friend's pleasure, and he gazed at Hiccup with affection and began to purr as the boy whispered endearments and exclamations of pleasure to him while he thrust his hips until he came.
Hiccup withdrew and watched as the flexible dragon licked Hiccup's dick clean, and then lapped at his own slit, sloppy with Hiccup's precious small load. The dragon became turned on, his great cock expanding and emerging from the slit while Toothless licked the remainder of Hiccup's cum from his own penis. Then Hiccup took over.
Since the discovery of the delectable edibility of dragon cum, Hiccup had begun to suck his friend's dick. Squeamishness was banished by his new found appetite for the bounty that the formerly unattractive organ could offer him. He closed his lips around the pointed tip, and could only get a few inches in, tickling the back of his throat. The dragon's cock was tapered, and the boy could barely get half of it into his mouth. Any further than that, and his teeth scraped too hard on his friend's sensitive, thin skin. But it was plenty to satisfy the dragon, and Hiccup needed only the tip to drink the sweet ambrosia from. But this time, as Toothless neared climax something different happened.
Hiccup first felt it with his hands, then he opened his eyes and observed the final feature of the dragon's sexual maturity. At the base of his big red organ... Toothless now sported a knot.
Hiccup's heart pounded, more than a little bit intimidated but excited to try it out. However, the knot was already full and there was no way it would get into Hiccup's asshole like that. The only thing that could relieve the knot at this point was for Toothless to climax. Hiccup would have to wait and try to take the knot next time. Meanwhile, he was more than happy to fill his belly as planned. He sucked the tip and stroked the slick shaft with both hands until the dragon called out with his signature bleat.
Hiccup pressed his stretched lips around the tip and held on with his hands for dear life. The spongy flesh around the dragon's baculum, the bone at the core of the penis of many mammals, swelled to hardness like his knot and began to flex and pulse. The cum pumped forth, spurting into Hiccup's hungry mouth. He swallowed desperately, trying to drink it all for once. But of course it was too much. The spray came with too much force and too much volume. Hiccup's cheeks expanded, and sweet semen burst from around his lips, and even out of his nose. The boy held his breath and gulped. The hot fluid flowed down his throat, filling his tummy. The cum that escaped ran down the dragon's cock, coating Hiccup's hands in pink. At last, Hiccup needed a breath and he released the tip with a ragged gasp. His chest heaved and he coughed and blew to clear his sinuses while the massive organ continued to pump two more jets of cum, splattering Hiccup's face and chest. Hiccup trembled with excitement and swiped his hand over his skin, harvesting the lost cum and shoveling it into his mouth. Smearing it over his face, lost to all articulate thought and driven only to ingest more. More. More.
The next day was torture for Hiccup, waiting through his daily routine until he was able to be alone with Toothless again. After work, the best friends fled to their cove. Hiccup immediately stripped naked and presented his desperate ass to Toothless. The dragon lapped at the boy's opening with his tongue until Hiccup begged Toothless to please just shove it in.
The dragon complied, responding to the boy's lust and elevated emotional state. His cock slid out of its sheath and he thrust it directly into Hiccup's body.
The sting sent shock waves through Hiccup, igniting his skin all over. Then a warm wave of pleasure crested through, rolling over the pain. He grunted and growled through his teeth, becoming more animal than the dragon, and he slammed his hips back against his best friend's out-strokes. Hiccup couldn't allow the knot to bloom outside of him, if that happened he'd be denied. If the knot couldn't get out then of course it couldn't get in, either. It had to swell in the right place. It was the most important thing in Hiccup's world at the moment. He would have it. He needed it.
And then it happened. The blessed event. Hiccup felt an expanding near the base of the dragon's great prick. He shoved back, scrabbling at the earth with his fingers and knees. He let out a victorious cry halfway between a laugh and a sob. Toothless pressed back as hard as he could. Success! The knot filled inside the boy's chamber, and the dragon's turgid cock was trapped.
His moment of triumph achieved, Hiccup substantially relaxed. His muscles ached with the tension from his berserker state. He would have sunk to the ground and lay there limp, but now he was attached to his mate. The thrusting of the dragon's hips shook Hiccup like a rag doll, and he thrilled at his own helplessness. Toothless possessed him now, and nothing could break them apart until Hiccup was "bred". The dragon bleated.
"Oh, gods," Hiccup gasped, "Yes. Yes!"
Toothless came. That unstoppable force exploded within Hiccup. His guts were bathed in spurt after spurt of dragon cum. Rolling and gushing through chambers deeper than it had ever gone before. Prevented by the knot from escaping as it usually did, the hot gooey fluid had nowhere to go but further in. The pressure frightened Hiccup and for a moment he wondered if he had made a terrible mistake. But at last the eruptions ceased and the boy was safe.
He felt great. So incredible. The delicious pressure was a new sensation, absolutely fascinating, and a massive turn-on. Hiccup's belly was distended, tight and round.
Toothless settled onto his haunches, and awkwardly flipped onto his back as gently as he could. The boy was pulled along, briefly flailing through the air until the dragon settled on his back. Hiccup wound up sitting upright, held fast on the spindle that ran through him. He wriggled and twisted around on the dragon's cock to face his mate. He brushed his hands on his scraped raw knees, and examined his pot belly. He smiled a big happy grin at his best friend.
With extraordinary flexibility, the dragon curved his back and nudged Hiccup's round tummy with his snout. Hiccup chuckled, and patted the dragon. His cock was rock hard, and the dragon's forked tongue pinched and lapped at his aching member until the boy popped off, squirting across his soft tongue. Toothless purred and swallowed the delicious gift.
The dragon lay down and continued purring. The boy bent forward and lay against the dragon's skin as best as he could, stretching the base of the dragon's cock and pulling on the knot. They cuddled until the knot went down. when it had deflated enough to pass through Hiccup's ring, a great gush of cum was released. Hiccup whined and groaned as he was emptied out, the fluid rushing over his legs and down the dragon's flanks. The emptiness he felt now was as much of a shock as the inflation had been not so long ago. He was sad to lose that fullness, but he knew he could have it again tomorrow. He patted his friend affectionately and they both dozed off.
But eventually, waiting to get that fullness back wasn't enough. Hiccup got an idea. He took a block of soft wood and carved for himself an object looked vaguely like a mushroom, a cone with a round small tip that flared out to a wide bottom. There was a short stem attached that ended in a disc-like base. He applied several coats of smooth laquer, and he had an anal plug.
That completed, the next morning when Toothless fucked him they made sure that the dragon knotted outside of the boy. Hiccup squeezed his asshole as tightly as he could and was inflated. The pair struggled to replace the dragon's cock with the plug as smoothly as possible. Some of the huge load escaped, but Hiccup locked most of it inside.
Hiccup dressed and went about his day like that. Full of dragon cum, thrilled by a naughty secret. He could feel it slosh around in his guts when he walked, and frequently became erect thinking about sex and Toothless. It was bliss.
His friends noticed his belly, and made fun of what they thought was weight gain. Hiccup chuckled and agreed that he needed to lay off the dessert.
The truth was Hiccup's secret. His and his best friend's; Hiccup's trainee turned trainer. Toothless had supervised a strict but satisfying regimen of kinky pleasure, and Hiccup had come out the other side a fully-fledged and certified cumslut.
He wouldn't want it any other way.