Water Balloon of a Different Sort

The Starfall Islands were well known for the abundance of well-preserved ruins among them, although some on Rhea Island had ended up submerged in a lake over the time "The Ancients", as they'd come to be referred to, had been gone. Said lake was relatively shallow, however, making it feasible for confident divers to explore, even without diving gear of any kind.
One such diver could currently be seen walking on the bottom, having chosen not to swim: An anthropomorphic bright-green crocodile, wearing no gear - or clothing - of any sort. This crocodile, Vector, puffed some bubbles from his nostrils to partially relieve the discomfort forming in his lungs from his past 10 minutes of breathholding, about half of the longest he could handle. He made no move for the surface, despite it only being 20 or so feet above him; not only did he prefer walking instead of swimming, he liked to pretend he couldn't even swim at all. Whenever he needed air, he'd either walk all the way back to shore, or climb onto something tall enough that he could reach the surface.
"Mmh...Blblrp..." Another couple minutes, and as much as he enjoyed pushing himself, Vector decided it was high time he went back to breathe. Only now puffing his cheeks, he started to jog toward the shore, though he soon slowed back to simply walking. He'd have no issue reaching the surface long before he'd even risk running out of breath, so he took his time to enjoy the breathless feeling a while longer. Soon enough, his chest started heaving, and at the same time, he started getting aroused, dick slowly becoming erect.
Too soon, Vector was climbing the slope to the surface, a blush on his snout from both strain and arousal, just about to reach the air his lungs demanded. But, he hesitated. "Hmrk, blrblgh..." Getting an idea, he smirked, breaking the surface and...
"..."
Continuing to hold his breath. Even as he left the water entirely with a contracting chest, he didn't inhale, sitting down and keeping his cheeks puffed. Whether he held it underwater or not didn't make much difference to him, he enjoyed it regardless. This time, he decided to speed things up.
"Huffff..."
Exhaling most of what air he had left, his lack of oxygen now rapidly advanced, though it still took almost 20 seconds for a burning to take hold in his lungs. Vector nervously squirmed, groaning loudly and gripping his snout to keep it shut, seeing for himself as his blush started turning purple. "HMMM! MM-HRK-MMGH!" Vector started flopping his tail against the ground behind him and tightly shut his eyes, while his dick throbbed heavily, quickly nearing an orgasm just from being so desperate to breathe... But, he just couldn't hold on any longer, and released his snout. "HUUUAAAAA!" Finally, nearly a minute after he surfaced, Vector loudly gasped and panted, coughing a few times, blush returning to normal.
Finally calming down a while later, he muttered to himself, "Should've brought my stopwatch... Never gonna know how long that was..." He sighed, standing up again and starting toward the lake again, before seeing something strange in the distance. Some kind of reddish-purple thing floating in place... For the moment, Vector was more interested in whatever that thing was than the underwater ruins, and set off toward it.

At last, he arrived at the strange floating object, and could now make out much more detail. It was a robot of some sort, about twice his height, with a wide head on top and 5 "arms" coming from the base of said head, seeming to be holding the strange thing that had initially caught his attention, which also had a spike on its bottom. If the robot had noticed him, it didn't make it obvious, simply slowly bobbing up and down and drifting with the wind. Vector cautiously approached it, starting to hear a sort of aquatic ambience coming from the container it held. Even standing next to the robot, it still didn't react, and Vector put a hand on the container, continuing to be ignored. It felt like rubber, and had a bit of give to it. He pushed it, causing the whole robot to wobble for a few seconds before settling down. Clearly, that balloon-like container was full of water, but why did the robot have it?
Vector talked to himself as he theorized. "Maybe it's meant for water storage... Seems a bit excessive to make a robot for that, though. Water transport? ...No, don't think it can move under its own power..." He chuckled. "Seems like a pretty stupid robot, to me!", he said, and slapped its balloon-
Except, instead of actually hitting it, his hand went straight through the balloon's surface, and some kind of force started pulling him in! "What the- Crap, let go!" As always, the robot didn't react, and as Vector's arm was already pulled in up to the shoulder, he gasped deeply and held his breath just before his head was sucked in. It was only a moment after that that the rest of his body followed, and he was fully submerged in this strange robot's balloon.
A strong current rushed down from above, pinning Vector to the bottom for a few seconds. After that, he sat up and looked around, noticing that there was now substantially more room inside the balloon, seeming to have almost tripled in size. Finally, Vector understood the purpose of this robot. Oh, I get it! This was made to capture people and drown them inside it! Despite seemingly being in danger, Vector wasn't afraid, and gave a smug smile. Too bad it's not rated for guys like me! The material of this balloon would never hold up against his strength, he could break out no problem once he needed air. For now, he decided to make the most of the robot's aquatic confines while he could hold his breath.
There wasn't really anything going on with the balloon's interior, the only feature it really had being a small hole at the top, presumably where the extra water had come from and where his exhaled air would go. Without much to do, Vector simply laid back down to relax, setting his hands behind his head and slowly sliding his tail back and forth. 
As the minutes passed, he occasionally blew some bubbles to entertain himself, watching them float away and disappear through the hole. Around when the 11th minute hit, though, he'd started straining enough that he couldn't relax any more, fidgeting a bit and puffing his cheeks, his bubbling slowly getting less voluntary. "Mm...m..." Vector made no move to escape, however, sitting up again and closing his eyes, focusing on the urge to breathe as his chest started to heave. He wasn't sure where he could find another of these balloon robots, so he wanted to make this stay in one count, in case he couldn't get out without ruining it. Besides, he always enjoyed pushing his breathholding ability, and as he got hard, he felt like going especially far this time.
13 minutes in, Vector hopped off the bottom of the balloon and swam up to about the middle, slowly kicking to stay in place. "Mmmrbl, blublp!" Even as a chest convulsion forced out some air, he still had a smile on his blushing face, growing increasingly aroused as he continued refusing to go breathe. Although, another minute and a half later, he finally started to lose his composure, cheeks now looking as if they each held a grapefruit. Even now, Vector still didn't try to escape, his visibly-throbbing dick calling for his attention and distracting him. Another minute or two couldn't hurt, he just needed a bit of help.
"Mmmmblrblrbl..." With a bubbly moan, and without caring about the air loss, he started jacking off. It certainly didn't help with his significant lack of oxygen, but it made it easier to handle, and he felt he could last a while longer, now. He tightly shut his eyes, curling inward slightly and holding his snout, his lungs now starting to burn.
Even with the pleasure helping him hold on, a minute later, Vector couldn't take it any more. All the idle bubbling he'd done earlier had wasted a lot of air, significantly cutting down on how long he could hold his breath, and now he felt he was nearing his limit. "MMMRGH! HM-MMM!" Flailing for a moment, he quickly swam to the nearest edge of the balloon and started beating against it... Except, nothing happened. D-damn it, I was kinda banking on this being easy! The material was smooth enough that he couldn't get a grip on it, so biting through was out of the question as well.
Frantically looking around, shivering in place with both hands on his purple-tinted snout, he quickly remember the little hole at the top of the balloon. It was far too small for him to fit through, and didn't seem to lead to air, but it was a pretty clear weak point. Vector bolted straight to it, released his snout to shove some fingers into the hole, and tried to pull it apart. Even giving it everything he had, though, there wasn't even any creaking, metallic or otherwise. "HGLK, BLURBL-MM!" His chest heavily convulsed, inflating his cheeks to the size of basketballs and pushing out another cluster of bubbles before he could hold his snout shut, which he did immediately after. It was rare that he held his breath this long, and he wanted no part of it!
Now starting to panic, Vector just repeatedly punched around the hole with his free hand, hoping that maybe it would accomplish something, but still, nothing happened. With his blush turning blue, he gave up his ineffective attack against the robot, curling up again and gripping his snout with both hands. "HRK, GHK...SNRFKH!" His eyes widened, cheeks now the same size as his head, as he sucked in through his nostrils, having forgotten to cover them. The water burned as it flowed into him, and although it wasn't much, as he felt it settle into his lungs, his shivering turned to desperate shaking. There was no doubt about it, now; he was drowning!
Adjusting his grip to now cover his nostrils, Vector did everything he could to keep holding his breath, or at least suffocate himself so more water couldn't get in, but as he frantically kicked, the water sloshing inside him, sensation in his cock started to surge. Having not actually achieved an orgasm in this breathhold - if it could still be called that - he was incredibly horny, though was too panicked to really notice. So desperately needing air, and with wet lungs, his arousal rapidly built on its own, now culminating in a powerful hands-free orgasm.
"HKGH, KHK, KABLURBABL HAKBLRGL!" At the same time as cum started being shot into the water, Vector couldn't stop himself from coughing up the water he'd inhaled, quickly emptying his lungs of both water and air. Humping at the water and spurting more cum, he tried to hold back, but there was only really one thing he could do now.
"RK, G-GHUUUAAA-AGLK!" His maw opened wide, and water flooded into him as he forcefully gasped, his orgasm intensifying. With both hands now tightly gripping his neck, Vector harshly choked and gasped, quickly forcing out the last of his air and even more cum, now starting to somewhat cloud the water in front of him. Barely even noticing his prolonged orgasm, he scrambled back up against the top, having sank some distance during his struggles, and tried to put his lips around the hole and suck in. His bubbles had gone up into it, so maybe he could gasp some air through it? But, no, all he got was yet another lungful of water, and he went right back to choking.
Finally coming down from his orgasm, though with his dick still throbbing, Vector swam to an edge of the balloon and started hitting it, though with his coordination starting to suffer it was more like frantic slapping. He hadn't noticed before, but the material was somewhat reflective, and he could see his blue blush slowly spreading across his panicked face before he turned away with a hand going back to his neck. "GLUGLUK! HUU, HUUAA!" Vector's choking was turning to just heavy panting as his energy faded, although it certainly didn't feel any better.
Pushing off the edge, he struggled over to the opposite side and tried hitting it again, vision starting to dim. "G-GHUUH, HUUUAP!" Another gasp of water, and this time he held it, puffing his cheeks back to the size of his head. It made no real difference, it wasn't like he was getting any oxygen doing so, but it was marginally better than just continuing to gasp. "Grrghl...Hic! Hic, mmn-hicp!" His lungs tried to reject the water, rebelling with forceful hiccups, and Vector held his snout shut again, giving up on hitting the balloon's edge. A few seconds later, a wave of fatigue washed over him, his adrenaline rush ending and making him feel as if he were about to fall asleep. "Mmmh...Bluuugh..." As his body relaxed, his hands fell from his snout and he exhaled the water he'd been holding in, resuming his water breathing and starting to sink.
With his face now fully blue, Vector bumped against the bottom of the balloon, his eyes lidded as he laid on his back. "hhhh....hnnglurgl..." He was utterly exhausted, to a degree he'd never been before, but forced himself to sit up, slowly looking around with a dopey smile, maw hanging open. Breathing the water was starting to actually feel good, although he'd forgotten it wasn't air at this point. "...nnnghuhuh..." As his body slowly shut down, a pleasant tingling set in, and he happily rubbed himself as he started going numb.
There was one part of him he could still feel just fine, however: His cock, still fully erect and throbbing with his slowing heartbeat. A-alright, ffine...quick jjack-off, thhen I'll ss...sleep... Forcing himself to move, Vector grabbed his dick and started stroking. For about 30 seconds, he kept at this, but soon it started taking some effort to stay awake. "......ghuuua...." He realized he'd stopped breathing for a while, and gasped to make up for it. Sso tired...mmaybe I....mmm... He slowly slumped forward, but caught himself and forced his way back to awareness. This repeated a couple times, his body just about ready to give out and beginning to tint blue all over, until Vector finally felt an orgasm building up. "huuh, huuuhh, huuup!" After a bit of panting, he held another watery breath, though didn't puff his cheeks quite as much as before. Just after, his cock spasmed and once again shot a load into the water.
"hmmmgh...HRMGRGL!" Vector tilted his head back, rubbing his chest with his free hand and continuing to jack off, before he finally remembered where he was, and more importantly, what he was breathing. "GARGLURGLK! HURGLARGL!" Grabbing his neck again, he started thrashing just as fiercely as he had when he'd first started drowning, then frantically swam straight up, leaving a trail of cum. Even though he knew there was no hope of escaping on his own, Vector's body went into autopilot, dashing against an edge once again and punching at it, gargling a near unintelligible cry for help. "GLURK, HEGLP! HUUA, HG-HELP MME!" The only ones to hear it were the robot he was stuck in, and himself, and the robot certainly didn't care.
His energy was already rapidly running out again, and his punches slowed to weak smacks, then nothing at all as he started sinking again. While his orgasm was still going, he'd run dry of cum, dick still jolting as if it were continuing to spurt. Realizing he was back at the bottom again, Vector tried to swim up, but found he lacked the strength to move his limbs. He barely managed to lift his head instead, looking along his blue body. His purple dick was still fully erect and trying to cum, and his chest didn't expand or contract, his body having finally given up trying to breathe. Lightly shuddering, his head fell back and he looked straight up, barely able to see despite his eyes being open. ".....mnh...." Vector began drifting into unconsciousness, and didn't have the energy to fight back any longer, simply allowing himself to pass out.
The now-blue crocodile laid motionless within the balloon, his overtaxed heart trying to keep beating for a while longer, until finally even that ran out of energy and came to a stop. The robot noted this, waited another few minutes to be sure Vector really was dead, then ejected his body out onto the ground and returned to its previous size, ready for another victim.