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Introduction:

Sister and Brother explore a cave in a foreign country. Brother needs "medical" help. Sister to the rescue..

It's all fun and games until someone's cock becomes out of control for medical reasons. Especially if that someone is in the family.

Kristen learned that the hard way.

What began as a family trip to Thailand turned into something else when they went to an exotic beach. Her parents were the brainy types, so they spent their morning with a group of other tourists and a Thai tour guide who was an expert in local geology and the ecosystem.

She and her brother, however, were ordinary college students with ordinary college needs, looking to swim and have fun. Kristen wore a sexy bikini. Matt wore swimming trunks. They'd been on plenty of family vacations together so they were used to seeing each other in swimwear.

They did some light swimming in the shallow end of the water where the waves hit the sand, getting warmed up for a deeper swim to follow.

"Feel like a race?" Matt grinned.

She grinned back. "Name it."

Being on the college volleyball team had really honed her physique over the past year. She was certain it would give her some kind of competitive edge in their everlasting sibling rivalry. She always loved putting her brother in his place, but it was only occasionally that she got to be the victor. Today, she was in an energetic mood. Confidence was flowing through her blood. Yes, she was up for any challenge.

"Let's see who can swim against the tide fastest," he said, pointing to where the water changed color. "Just up to there. Nothing dangerous. Then we swim back."

"What if I win?"

"You won't. But the winner gets to sleep on the bed next to the window for the rest of the trip. No more alternating."

"Hmm..." she pretended to think. "You're on!"

Kristen dove into the water first and went full force against the oncoming waves. All that working out at college was really paying off. She didn't have to check if her brother was on her tail; but she knew he wasn't far behind. They were both competitive, after all.

When she came up for air, she saw that her brother was catching up with her. She pushed harder. She had to win this.

Unfortunately for Kristen, her brother's strength and stamina gave him a big edge. She had better technique, but Matt had better muscles. He won this time, but Kristen was right behind.

The race ended further from the starting point than anticipated, and they were both gasping for air.

"Lucky you," Kristen said laughing as they trod water.

"Damn, you're getting good," he said back, still gasping for air. He glanced over Kristen's shoulder. "Holy shit. Look over there."

They looked to the right and saw a series of massive rocks and boulders which appeared to have formed a small hill. It was unlike anything they had ever seen back in America.

"Isn't that where Mom and Dad went?" Kristen asked. "On that tour."

"I think so. It's kind of dangerous apparently, so if you're not a local, you have to go with a tour guide."

Kristen couldn't take her eyes off it. "What's so dangerous about it?"

"Caves, I think."

"Bummer. We should have gone with them."

"We can still go," he said defiantly. "It'll be our own private tour."

"Sure, if you're up for it," she replied, quick to rise to the challenge.

"I am. But are you out of breath?"

She splashed water at his face. "Let's go slow this time. My heart is still pounding."

"Mine too."

They swam side-by-side, at a much more leisurely pace. The closer they got to their destination, the more excited they became. This was what Thailand was all about. Adventure.

After a 5-minute swim, they were almost there. Their arms were tired, but they knew they'd be okay after some rest when they reached their goal.

"I don't see anyone," Kristen said as she emerged from the water. "It's kind of scary here."

"Who knows. They might be in a deep cave somewhere. There's a number of them if I'm not mistaken."

"I'd love to have a peek. I've never seen a cave before."

"Ahh!!!" Matt hollered suddenly. "Shit!"

He jumped up as soon as he reached the shore and limped out of the water.

"That's not funny!" Kristen screamed.

"Something bit me," he said as he inspected his left thigh.

"Really?"

"Look."

Kristen could see two small holes on his left thigh. The skin was red, but it wasn't bleeding.

"Jesus. What the hell was it?"

"I didn't see it," he replied. "It got me and swam away."

"Should we swim back to the resort? It might be serious."

"I need a little rest before I can swim back. How about you?"

"I need rest too," she said.

"In that case, we might as well check out a cave while we're here. It beats sitting around doing nothing."

"Can you walk?"

"My leg feels fine," he replied. "It's probably nothing."

Kristen grinned, eyes sparkling. "In that case, I'll race you!"

She immediately positioned herself to sprint to the nearest cave.

"Hey! Same time!" Matt said.

"I'm only joking. Come on, let's stroll to that cave over there, then we can go back. I'm worried about that bite. We should get you some treatment. Afterall, we don't know what it is."

They walked over to a nearby cave entrance. It was a small one. Narrow. There was light shining inside, so there were probably other openings.

After a short while inside, they came to a dead end and saw a hole down on the bottom of a cave wall. It appeared to be well lit on the other side of that hole.

Kristen bent down to peer through the hole.

"What's on the other side?" Matt asked.

"It looks stunning," she replied. "I don't know how to describe it, but it looks like a pond with these crystal things which naturally formed from the top. It seems like sunlight is filtering into the space too."

"Well, let's squeeze through the tunnel and go have a look."

"Are you sure you'll fit inside? Because I know I'll fit in there. I'm lean and slender. You may be in shape, but you have broad shoulders and muscles."

Matt knelt down beside her and peered inside. "It'll be super tight, but I'll fit. It looks amazing in there."

"You're sure you'll fit?" she persisted. "You're sure, sure? Positively sure? Because if you get stuck in that tunnel, we're screwed."

He kept analyzing with his eyes. "I think I can make it in. I'll go first. If I get stuck, which I won't, then you can pull me out."

"What a joy."

"Here it goes."

Matt crawled on the wet surface and made his way into the tiny space. He held his arms forward and exhaled in an effort to make his body slimmer. He felt as though the air was being squeezed out of his lungs at one point, but he made it.

Once on the other side, he stood up and breathed deeply. Then he looked down again.

"Are you coming?" he asked through the hole. "It's really amazing in here."

"Yeah, hang on."

Kristen performed the same maneuver. It took much less effort, but it was still a mission. While her slender hips and torso were an easy fit, her tits felt plenty of discomfort as they pressed against the rocky surface.

Once they were both inside, the siblings marveled at the exotic cave. It was unlike anything they had ever seen on tv. They seemed to be in the midst of a cave complex. It was like a maze. There were cave entrances in all directions.

"Let's not even think about exploring more," Kristen said. "We'd get lost."

"I know. This is overwhelming enough. God, look at this place."

Their eyes marveled at the structure which was created entirely by nature. They took a few moments to walk around the pond area and peek inside several of the cave and tunnel entrances. It was simply majestic.

"Ouch," Matt said suddenly, limping a little bit more.

"Are you okay? Is it hurting?"

With concern, she touched her brother's bare shoulder, holding on to him to make sure he wouldn't fall.

"I feel weird," he said. "I don't know, it's like a pressure is building up inside of me."

"Can you swim back?"

"I don’t know. I have to sit down."

"Shit," she said. "We better go before your leg cramps or something. We'll swim close together. If your leg hurts too badly, then I can help you swim on your left side."

"Thanks. You're the best."

They went back to the tiny tunnel from which they came. Matt attempted to go through. He lowered himself, kept his arms forward, and got ready to slither back to the other side.

Everything seemed to be going smoothly--- until he was halfway through. He gave a small yelp of pain.

"Are you okay?" Kristen asked, keenly aware that something was wrong.

"Pull me back! Pull me back!" Matt was shouting in desperation.

She grabbed her brother's ankles and did her best to pull him out of the tunnel without hurting him. Mercifully, the retreat was smooth.

"What happened?" she asked.

"It's nothing."

Clearly it was something. As he sat on the ground, he adjusted his swimming trunks more thoroughly this time. He dug his fingers in the front and shifted things around.

"Are you... hard?" she asked, which sounded more like an accusation.

"What? No. Are you kidding?"

He sat there, still having a hard time adjusting himself.

Finally, he confessed. "A little. I don't know what's going on. It's like, I'm not aroused, but there it is."

He gestured down to his crotch area.

Kristen raised an eyebrow. "You're not aroused, but your dick is hard?"

"You wouldn't understand."

"You're right. I don't. All I know is that caves are dangerous places, you've already exerted a lot of physical energy by swimming here, and now you're sporting an erection?"

He scoffed. "You think I'm doing this on purpose?"

"Are you?"

"Let's just try again," he sighed.

"No. Not yet. I don't want you to hurt yourself. I mean, is your dick really so big that you can't squeeze through?"

"It's decently-sized," he answered through gritted teeth, almost offended that she'd ask something like that. "Trying to squeeze through hurts like hell. Just imagine a rock being pressed tightly against your... nevermind. You get the idea."

"I can imagine. The rough surface was tough on my breasts too, but it was still much easier for me to fit."

"Should we try looking for another exit? There's light and plenty of other caves."

"No way, I'm scared," she said firmly.

"So is it... are you... still hard?" she asked cautiously.

He sighed. "It's throbbing, actually. I also feel kind of light-headed, like my blood pressure is high."

Kristen squinted her eyes as she thought. She had taken plenty of health classes in college and had read countless articles on the human body over the years.

Suddenly, it came to her.

"Holy crap, Matt, do you know what this means?" she exclaimed at last.

"What?"

"That bite. Whatever bit you might have released a toxin in your body which is causing your erection. I read about something similar happening to someone after an insect bite a few years ago."

He checked his wound. "Oh shit, you're right. Look."

The punctures on his thigh turned even more red, but still wasn't bleeding, suggesting that something had indeed been injected into him.

"Now what?" she asked.

"I don't know."

"Should I swim back myself and bring in the experts?"

"Do you realize how humiliating that would be?" he asked. "Besides, I think it'll go away soon."

"You wish. If I remember the article correctly, the erection could last for hours."

"Damn, are you serious?"

"You tell me," she said. "It's your cock. You still look flustered."

"It's still aching."

"Can you walk?"

He shook is head. "Not sure, I’m lightheaded."

Kristen suddenly giggled at the embarrassing image of her brother having to walk around with a hard cock bulging through his swimming trunks.

"Too bad," she said, amused. "We have no choice but to try and find an alternate route. Nothing dangerous. But I'm sure there's a safe way out of here. Then we'll swim back to the beach. I hope your 'issue' won't hamper you while you're in the water."

Matt slowly stood up and there was a blatant bulge in his shorts. The head of his dick poked out and his shaft was outlined against his wet swimming trunks.

"Hmm..." Kristen said, almost licking her lips.

He covered himself with his hands. "Let's go."

They decided on the nearest cave for their first attempt at finding a proper exit route. There was some sunlight, so hopefully this would lead outside. All the while, Kristen was smirking and looking back to steal glances at her brother's bulge, making him blush and do his best to hide it while walking.

She stopped in her tracks suddenly.

"Wait," she whispered. "Shhh..."

They stood still for a few seconds. Neither of them made a sound.

"What is it?" Matt whispered in a low voice.

"I thought I heard something."

They kept quiet a few seconds longer.

A faint sound echoed from the caves:

'...all of which formed thousands of years ago...'

Their eyes widened when they heard the voice.

"The tour guide?" she whispered.

"I think so."

"But where?"

"It's an echo," he replied. "They could be anywhere."

"We could shout and try to join their group?"

He pointed to his crotch. "Imagine if they saw this. They'd think I'm a pervert."

"But your health, Matt. The tour guide might be able to assist."

"I have a really hard erection. Mom and Dad might think we were having sex inside this cave if they saw me like this."

Kristen's jaw nearly dropped. "Crap, you're right. Quick, let's go back."

They rushed back to the tiny space from which they came. Unfortunately, the small hole was the same size, and Matt's erection was still bulging.

"I'll just sacrifice myself," he sighed. "You swim back to the shore yourself. I'll try to meet up with the tour group and explain that a creature bit me."

"Yeah right. We're supposed to stick together. Mom and Dad know that we wouldn't separate. Not in a foreign country. We'd certainly split up in America, but we'd never split up in Thailand."

"You're right."

"Now what?" she asked.

"I’m thinking.”

"What if you... you know... take care of it?"

"Huh?"

"Jerk off!”

He blushed. "It could work. Did you read about that in the article you mentioned?"

"No. The article made no mention of relief. Just that the erection lasted for hours."

"You should crawl out and wait outside. I'll relieve myself, then I'll follow you."

She raised an eyebrow. "But what if it doesn't work? You'll be stuck here by yourself."

"Good point."

"Just cum," she said bluntly. "It'll be fine."

"Are you sure?"

"Then get to it," she said hurriedly.

"But that means you'll see my dick."

"Your balls too," she added.

He lifted an eyebrow. "You don't mind?"

"Like you said a moment ago, if Mom and Dad see this, they might think we were fucking in here."

"Oh god."

He stuck his fingers underneath the elastic of the swimming trunks.

"Need help?" she asked.

"Yes, my arms are weak."

Kristen reached over and yanked her brother's swimming trunks down. She expected to see a hard cock. What she didn't expect was a hard cock swinging back and nearly hitting her in the face. She moved her head to the side swiftly like she was playing dodgeball.

"Oh wow," she gasped. "That looks serious."

She stared at his cock, which curved upwards and was swollen to the point where it nearly turned a shade of red.

"I know. It's way harder than usual. Do you know anything about this?"

Kristen inspected it closer. "Hmm. Wiggle it."

"How?"

"Move it, up and down."

Matt bounced up and down, moving his cock as his sister requested.

"Now side to side," she commanded.

Matt stood in place and continuously turned his waist so that his cock waved from side to side.

"Any thoughts?" he asked.

She grinned cheekily, "It's a super hard dick."

"Thanks for the expert advice."

"Hey, I'm doing the best I can. Now let's get it done. I'll assist you however I can."

"Fine, and remember, this is your plan."

"But it's your cock," she quipped.

"Touche."

Matt grabbed his steel hard cock. He start to pump his hand up and down, and then stopped.

“What’s wrong?” Kristen questioned with concern.

“My hands are weak. I’m not sure I can make it cum.”

Kristen got up and went over to the other side of the cave. She kept her ears peeled and listened attentively to the echoes.

Sure enough, she heard the Thai tour guide speaking from afar. The tour guide made a joke and the group of tourists laughed. Most unsettling of all, she recognized the laughter of her parents.

And they were headed this way!

She rushed back to her naked brother and his hard cock.

"I think they're coming," she hissed.

"I’ll try again.”

"I don't want to damage your beautiful cock," she said. "Err... I meant... you know what I meant. Anyway, I have a plan."

"What is it?"

"Remember when I lost the race? Then you won the best bed? If I got you out of this mess, with your cock still intact and feeling better than ever, will you give me the bed?"

"Hell yeah. What's the plan?"

"It requires you to relax," she said.

Kristen wrapped her fingers around the hard cock and she gave it a loving stroke. Up and down.

"Ummm... what are you doing?"

She kept stroking. "I'm getting you out of here. Face it, if you don't cum, you're trapped. Your body is too big and the current state of your dick makes it impossible for you to squeeze through that hole."

"You're so bad."

"That's no way to speak to your caregiver."

She kept on stroking her helpless brother's cock using a simple handjob technique. Under normal circumstances, her traditional clench and stroke would have made a guy cum in 10 minutes or less. With the effects of the toxin, she'd likely require more effort.

Time was of the essence and each second was precious.

"How long will it take?" she asked. "How about if I go faster?"

She stroked faster and harder.

"Not sure," he moaned. "Damn, that feels good."

As she stroked, feeling Matt's cock pulse in her hand, she made other calculations as well.

"I need to preserve my arm strength," she said. "If I keep jerking you like this, it'll be harder to swim back."

"Do whatever you need," he replied, enjoying the experience.

"You better appreciate this."

"Of course, I do."

Kristen bent down and fulfilled a longtime curiosity and dark fetish by taking her brother's dick into her mouth. As tense as the situation was, this was also the perfect pretext to suck him off.

She closed her lips around the stiff shaft and had her way with it. She sucked it tightly and bobbed her head while stroking it with her tongue. She could feel it pulsating and throbbing in her mouth, far more than any other cock she's ever had in her mouth. In a way, she was glad Matt was bitten by whatever it was. She was curious as to what that toxin was.

His moans echoed in the cave. As did Kristen's sucking and slurping. It was the first time she was able to hear herself suck so vividly and it was such a turn on. But listening to Matt in desperate sexual despair because of what her mouth was doing to him was the ultimate turn-on.

"Oh God, I’m close Kris," he said in a low voice. "I feel like I'm going to burst!”

She spit the cock out for a moment. "You haven't earned full-on mouth cleaning privileges yet.."

"Okay," he didn’t complain.

"You're the best cocksu--- I mean, you're the best sister alive."

She stroked hard and fast. "I know I am. The best sister. And the best cocksucker. Always remember that."

Then she went back to working her mouth around the shaft in an attempt to make him cum faster. She even took him deep in her throat because she knew that guys loved that. Her throat was the real 'tunnel' that men were interested in.

She almost gagged as she took it all the way to the back of her mouth, close to the center of her throat.

When she had the deepthroat, she held it, then listened. Laughter? In the background? The Thai tour guide must be a funny guy, and that gave her fair warning.

"They're coming," she hissed after spitting the dick out, freeing her throat in the process. "This isn’t working. Will my pussy help you cum faster?”

"Pussy usually works best, depending on how tight you are and how you work your hips."

"Done. Lay down.”

Those were Kristen's other specialties, aside from sucking and deepthroating a cock. Her pussy was tight and she learned how to fuck from other college girls. Perhaps this would be the stimulation her brother needed to speed up the orgasm.

She sat upright and climbed on her helpless brother's lap. She pulled the crotch of her bikini bottom aside and positioned her wet pussy above her brother's hard saliva-covered dick.

She held his hard cock upright with her fingers and slowly lowered herself onto him.

"We're going to fuck," she said matter-of-factly. "And you better cum. Fast. If we get caught, you're a dead man. Got it?"

"Yes, yes. We'll both be dead if our parents see this. Do it already."

She lowered herself and her labia wrapped around the dick. Although her pussy was tight, entry was easy because of how wet and aroused she was from doing all these rather dirty things with her vulnerable and needy brother.

By the time Matt's big dick had slid all the way inside of her pussy, they were both gasping in pleasure. Her hole was tight. The second tight hole which may well be the death of him.

She bucked her hips and began to ride him. She knew all the techniques of cock riding and pussy control. She learned about it online and from some of her slutty friends on the volleyball team. Who would have thought she'd ever these techniques on her own brother of all people? (Oh, how she had secretly hoped...)

Her hips gyrated hard and fast. In this position, and with the size of his dick, each thrust was hitting Kristen's elusive G-spot directly. She wasn't sure who'd cum first, herself, or her brother.



Why not both at the same time?

She clenched tightly and rode as fast as she could. Kristen was having the time of her life with that cock.

"Oh fuck, his cock feels so good," she whispered to herself, eyes closed, digging her fingers into his stomach.

"What was that?" he whispered back.

"Oh, nothing. Hurry up."

There was one last trick in Kristen's arsenal. She knew it could be painful for both of them, but as the faint sounds of talking and laughter grew louder, she knew it had to be done.

She practically bounced on her brother's cock, her athletic legs pushing her body up and down. Each bounce hit her G-spot. It was like something out of a professional porn shoot. And it was working.

After the tenth bounce on his cock, Kristen came first. “Matt.. I’m cumming!!”

Her pussy and G-spot were so overwhelmed that she had to clench her jaw to keep herself from screaming at the top of her lungs. If she had, and the tour group heard it, then they'd really be fucked.

Instead, she made short, suppressed whimpering noises. Her jaw and eyes were squeezed shut. Her toes curled as she squirted a small river all over her brother's crotch.

"Hmm..." she whispered, her fingers digging even deeper into her brother's stomach.

She gave two more bounces and saw Matt's body jerk.

“Kris you did it. I’m going to spill. AAAAHHHHHH!!!!!” She felt a huge spurt of cum shoot inside of her body. She gave several more bounces on his cock, each one making him flood more cum inside of her.

They were both exhausted, sweaty, and in need of a long nap to recover from their unholy ordeal.

The voice of the Thai tour guide grew louder.

"And we are soon approaching the most exotic cave in this entire complex."

It was becoming too close for comfort. They'd be here at any moment.

"Holy fuck," she whispered.

Kristen climbed off her brother. It looked like a bottle of glue had been spilled all over them. A mixture of his cum and her squirt were everywhere.

As soon as she released him, Matt was able to stand up, his cock was shrinking, dripping semen on to the sand.

Kristen grabbed her brother's swimming trunks and headed for the opening. By the time they made it to the opening, Matt’s cock was back to normal. They both squeezed through the small opening. Once out, Kristen noticed the front of Matt’s body was coated in their sexual juices.

Right on time, too. They heard the tourist group enter that cave and marvel at the beauty of it. The siblings knew they had to pause and remain still for a moment, otherwise they'd be heard.

They listened to the tour guide show everyone around.

"Phenomenal as you can see..." the guide said before abruptly stopping. "It looks like creatures from the sea or land animals had gotten here before we did."

The tour group laughed at what they saw on the ground.

On the other side of the cave, the siblings looked at each other with mortified expressions on their faces.

Kristen mouthed the words, 'They're laughing at our cum puddle. Oh my god.'

'Let's go,' Matt mouthed quietly. 'Don't make a sound.'

The siblings tiptoed out of the cave. Once they were free on the sandy beach and open air, Matt put his swimming trunks back on. Kristen couldn't help but sneak a final peek at her brother's cock.

"Crap," she said. "We almost got caught by everyone."

"They saw our cum. Holy shit. Ha! Ha!"

Kristen smiled, "They all laughed, which means Mom and Dad laughed too, not knowing that the mess was ours. Anyway, race you back to the resort?"

"What do I get if I win?" he asked.

She pulled the front of her bikini down to show her pink nipples. Matt was stunned for a moment. Kristen took advantage of the situation and sprinted towards the ocean. Matt followed behind. The race was in full swing.

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