A bubbled contest gone wrong

It started with simple arm wrestling, as Rhett and Shorty tried to prove who was the more "alpha" of the two. With neither of them being satisfied, though, things slowly got more and more heated, and as they eventually started running out of ideas, they turned to more strange contests. Despite not being able to swim, and simply sinking like rocks underwater, they tried things like running as far along a riverbed as possible in one go, or taking turns walking deep into an underwater cave, marking a spot, and daring the other to go past it in an odd twist on "Chicken". Such games had led to a substantial improvement to their lung capacity, as well, both Rhett and Shorty now being able to hold a single breath for a record of almost 15 minutes, long enough that they could actually reach the deepest point of the flooded cave and even relax there for a couple minutes before needing to return. Once again, they would need to make things even more intense... But how?
Rhett and Shorty had gone hiking together, hoping to find the answer they were looking for in one of the few times they'd work together. With it still being fairly early in the day, the morning dew hadn't dried up yet, and seeing it reminded Shorty of something that could help the two of them.
"Hey, you ever heard of the Dewdrop Forest?"
"Yeah. I wish it was real, the stories make it sound pretty cool."
"It is real! I've been there, and there's stuff there that'll help me prove I'm better than you!"
"Don't give me that "My dad works at Nintendo" crap, it doesn't exist and you know it."
"It's real, I swear to god! I actually know how to get there from here, but it'll take a while."
"...If I agree to go, will you shut up about it once you get bored of leading me nowhere?"
"Yes, but I promise I'm not just wasting your time."
"Ugh, fine. Maybe we'll find something helpful on the way there that actually, you know, exists."

Hours passed, with Rhett slowly getting frustrated and impatient, until Shorty gave an update.
"Alright, we'll be pretty much there once we're over this hill."
"Fricken' finally, this damn spot just had to be this far away."
"I think it's actually good that it's so far, means no one's gonna mess with it. Anyway, we're here!"
"...H-holy crap, it's real..."
They'd arrived at the Dewdrop Forest. Enormous trees with suitably huge leaves towered above them, occasionally dripping giant water droplets that would usually splatter about on the ground, though sometimes they would stay intact. The place made it seem as if the two longnecks had shrunk without noticing.
"Okay, this is rad as hell, but how is this gonna help prove which of us is better?"
"Some of those water drops get even bigger than normal, there should be one around here somewhere..."
A few minutes of searching later, Shorty found what he was looking for: An indentation in the ground that held an especially huge water drop, seemingly about 10 feet in diameter. "Rhett, come here, I found one!"
"Yeah, it's a huge drop of water, what of it?"
"I've played around with these before, and it's really easy to get in and out of them. Watch this." Shorty picked up a nearby rock and lightly tossed it at the drop, which absorbed it. "We could use one of these to help prove who's cooler!"
"Oh, I think I've got it! We hop into there and stay as long as our lungs will let us, right?"
"Yep! Whoever leaves first loses. You up for it?"
"Hell yeah I am, looking forward to kicking your ass at this!"
"How about we make this more interesting? Whoever wins this is definitively the alpha, and that's the end of it."
"You got it. This whole thing has been going on way too damn long."
Rhett and Shorty started taking deep breaths, each planning on doing everything they could to outlast the other. Then, as they started feeling lightheaded, they both inhaled as much as they could, held it, glanced at each other with determined smiles framed by their puffed cheeks, and walked into the water drop with a shlup. Shorty swim-walked to the opposite edge of the drop and leaned against it, while Rhett just sat down where he'd entered. With that, their challenge had begun...

Nothing eventful happened for quite a while, occasional bubbles dribbling from the dinos' nostrils as the minutes ticked by and they began feeling a slight urge to breathe. At the 8th minute, though, things started getting interesting, Rhett and Shorty beginning to slowly inflate their cheeks further as their chests started heaving and contracting. Rhett nervously looked behind him at the air less than a foot away, starting to consider giving up... Though, noticing Shorty grinning at him gave him the determination to stay put, and Rhett shook his head before laying down to look at the distorted sky outside the water drop, trying to distract himself from his need to breathe.
The 10th minute began, and as the dinos' breathless grunts and groans became audible to each other, they both started getting aroused. It was rare that they'd push their holds this far, but knowing what was at stake, they were both willing to go as far as it would take, at least for now. Rhett sat up and put a hand on his chest, propping himself up with the other, while Shorty held his nostrils shut and closed his eyes.
"...Mm...Mrph..."
Another minute. Now fully erect, Rhett and Shorty blushed from both arousal and the strain of their 11 minute breathhold. The discomfort in their lungs began slowly transitioning to a desperate burning feeling, and their cheeks were looking more akin to basketballs, yet, still, neither of them even considered giving up.
"Hmgh, mrk..."
With two more minutes of slowly increasing struggles, their strained groans turning to pained whines, they each tried to cover their mouth, little bubbles seeping between their lips anyway. Their blushes had turned purple, their cheeks grown even bigger, and they nervously looked at each other. D-damn it, just g-give up already! Rhett thought. Shorty, however, was doing a better job of keeping his composure for now. A-any second now... He'll have to b-breathe, then I can breathe right after...
"Mm-mmm! Mmblrbl!"
Neither gave up, and as the 14th minute started, Rhett couldn't help but move a hand from his mouth to jack off, his cheeks beginning to repeatedly deflate and reinflate as he started rebreathing his nigh-useless air. Shorty started rebreathing as well, though kept both hands on his mouth for the moment. With both of them shivering continuously and their blushes turning blue, though, it was clear that they were finally nearing the end of their challenge.
"Hmrg, hmm, MMM!"
15 and a half minutes. Both dinos had pushed themselves past their previous best times, and at last, one of them gave in. Whipping around to face the nearest edge of the water drop, Shorty started frantically pushing against it as he struggled to escape. Only in this moment did he realize he didn't really have a plan in mind for how to get out. Rhett briefly gave a pained smile as he watched Shorty give up, before recognizing what the issue was, jumping to his feet and smacking at the drop it turned out they were stuck in.
Their panicked struggles went on for another minute, blue blushes beginning to spread across their faces as their cheeks started to get a couple feet wide on each internal exhale. Loud whines and burbly, unanswered cries for help could be heard as the pain in Rhett and Shorty's lungs got to the point that they considered just breathing, thinking that even drowning couldn't be as bad as continuing to hold onto what air they had left.
"GMRKH! HMMGLBL!"
"HBLELP! GEBLT UBLS OUBLT OBLF HBLERE! MM!"
Rhett briefly lost his balance as something he stepped on slipped out from under him, and he looked down to see what it was. The rock that Shorty had tossed in earlier! Wasting no time, Rhett snatched it up and started hitting the water drop with it, hoping for better results. It wasn't long before Shorty noticed Rhett's plan, swim-running over to join him, holding onto his hand to try to get more force behind their hits against the water drop.
About thirty seconds passed, and with an especially strong push, the rock, and only the rock, slipped out of the drop and landed outside! "GABLAH, FUBLCK YBL-HMRBL!" Rhett's bubbled insult to the inanimate object was cut off as he covered his mouth again, doubling over and tightly shutting his eyes as he closed in on his breathholding limit. His cheeks inflated even bigger, to the point that Shorty had to step back a bit to avoid pressing on them, and Rhett's nostrils flared.
SSNRKH
Rhett's eyes went wide and his body began shaking even more fiercely as some water rushed down his throat and into his lungs. He managed to keep himself from coughing, knowing that if he did, he'd lose what air he had left and have no choice but to inhale again. Strangely, the sensation of water moving around in his lungs was driving his dick wild, heavily throbbing on the edge of an orgasm and spurting pre.
He wouldn't be the only one drowning for long. Shorty shuddered, grabbing his neck and arching his back, mouth opening wide...
HHHUUUAAA-KAGLURGLK!
Unlike Rhett, Shorty immediately coughed out a cloud of bubbles, then gasped again. As he choked, his dick quickly got so hard it started aching, and he could feel himself rapidly approaching an orgasm. At about this time, Rhett couldn't hold his watery breath any more, coughing up little bursts of bubbles and finally inhaling water a second time. His arousal surged as well, and having already been so close to an orgasm, he hit one right then and there. Humping at the water, Rhett gave a loud, gurgling moan as he spurted a good amount of cum. The pleasure distracted him from the situation, but only briefly, before the pain outweighed it and he went back to desperately choking, still in an orgasm. Shorty, meanwhile, stumbled and fell onto his back, both hands on his neck as he writhed about on the ground, still loudly hacking and gasping.
Finally coming down from his orgasm, and with Shorty in no state to help, Rhett started banging on the edges of the water drop once again, though only with one hand, keeping the other on his neck. He was beginning to lose any hope of escaping, but he continued regardless, not having any better ideas.
A good minute passed like this, the two dinos' faces now fully blue with nothing but water left in their lungs. Shorty arched back again, his arousal finally reaching the tipping point as he came, momentarily holding in a breath of water at the same time, puffing his cheeks a couple feet wide, before exhaling again and resuming his desperate gasps. Rhett was still hitting the sides of the drop, now managing to use both hands for it as he tried his best to gargle out a plead for help. "GH-GHAGH, HUUELP! SHKH-SOME-HLK-ONE HEKH, HELLP!"
His shouts went unheard, and as the minutes dragged on, he and Shorty started to calm down. Not because the situation was getting any less dire, but rather, the opposite, as the extreme lack of oxygen slowly sapped their energy. Rhett slumped against the side of the water drop face-first and slid down it to lay on the ground, while Shorty finally managed to compose himself enough to sit up, looking over at Rhett making a fool of himself and weakly chuckling.
Slowly, they both started to not care as much about the situation, but they still remembered why they'd come there, and something came to Shorty's mind. "...B-bhet I kh...cann hhold o-hic-on ll...loonger...ulp...thhanyouu..."
"Nn...nn-no yyou kh...kha...cann't..."
With that, a replacement challenge began, since it was quite unlikely that either of them would leave, willfully or not. The two drowned dinos sat across from each other, focusing on staying awake, freely breathing water as if they were fish, aside from the occasional waterlogged groan or hiccup. And, it went on for quite a long time. Indeed, they lasted so long it almost seemed like they had gills hidden somewhere on their bodies, the only sign that they weren't getting any oxygen being that they were each slowly gaining a blue tint.
A grand total of 10 minutes passed like this, Rhett and Shorty occasionally holding onto breaths of water for a few seconds, or rubbing themselves to try to wake up a bit. They'd both gotten fully erect again, and this time Shorty was the one to jack off. At least at first, before Rhett joined him not long after. This was making it quite a bit easier to hold onto consciousness, with each of them now having a reason to stay awake other than just their pride.
Yet another couple minutes ticked by, and despite the pleasure, Rhett and Shorty were starting to have a lot of trouble holding on. Their vision was heavily blurred and starting to dim, but they still did everything they could to keep from passing out for just a little longer.
"Mmmnngluuuhhh..." Rhett leaned back and moaned as loudly as his flooded lungs would allow as he came once again, so drowned that he could only fire off a few weak spurts. Suddenly, his whole body jolted as his instincts forced out one last panicked struggle for survival.
"HUGLK! GLUGH, HURGL, KAKH!" Putting both hands to his neck, Rhett choked and gasped almost as hard as he had when he'd first started drowning, his orgasm drastically intensifying as the last of his energy was finally being used up. Only 10 or so seconds went by before he quickly weakened again, slumping forward without even the strength to breathe. He subtly shivered a few more times, before going still with his eyes still half-open, his intense final orgasm reaching its end, as would his life before long.
Shorty managed to grin as he saw all this. ...ffinallyy beat yyou...assshole... Then, he too started choking again, cumming hard as he thrashed outside of his control for a few seconds, not quite remaining in this state for as long as Rhett had, but staying awake afterward for longer. Too weak to move, barely even able to think, he thought about whether it was worth dying to at last prove he was better than Rhett...h...hell...yyeahh... Finally satisfied with this victory, Shorty let go of his consciousness, his overtaxed and rather blue body finally submitting to the water after over half an hour of submersion.