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. Vector couldn't help but get a bit excited; despite fully knowing he could escape, there was no visible way out, and the concept of being trapped underwater was incredibly hot to him. Jumping off the bottom, which bulged out the balloon for a moment, he swam to roughly the middle, slowly kicking to stay in place and looking around to reaffirm he was "trapped", faking panic.
Now jacking off, he swam to one side and lightly beat a fist against the balloon's material, making sure to not use too much force so he wouldn't accidentally tear it open. Deciding to trade some air to potentially make this even better, Vector spoke into the water. "Sblomeblone hblelp! Ibl'm gblonnbla dblrowbln ibln tblhis tblhinblg!" Of course, he knew no one would hear him, but it still added to his fantasy.
He was already quickly approaching an orgasm, so he skipped ahead in his act, now pretending he was nearly out of breath, swimming back to the middle and gripping his snout. "Mm! Mmmrk!" He moaned into his cheeks, then did some more bubbletalking. "Nbl-nblo...Dbl-dblon't blreablthe..." Vector's arousal built up more and more, and soon enough, he passed the point of no return. He did his best to resist the orgasm for another few seconds, saying one last line. "...Ibl...Ibl-Ibl'm gblonnbla..." Then, he opened his maw wide, imagining himself to be gasping the water, and allowed his orgasm to start.
"GABLBALRRABLRBL!" With a loud, bubbly moan, Vector came hard, still masturbating with one hand while now holding his neck with the other, lightly thrashing as he pretended to drown. "GLURGL! AGLK!" He continued milking himself as he "choked", repeatedly spurting both cum and bubbles with each throb of his cock. As intense as his climax was, it finally started to taper off, and so did his false struggles, soon going limp and letting himself sink as if he'd run out of energy.
Now laying on the bottom again, he looked up with lidded eyes, letting his mouth hang open. "...glk...blbl..." In his fantasy, he'd fully drowned, and those bubbles were the last of the air in his now-flooded lungs. Vector imagined taking a few more breaths of water, then slowly closed his eyes, his "unconscious" body lying still.
A few seconds later, he opened his eyes again and sat up, a big smile on his face. That was his absolute best orgasm ever, he was certain of it! "Mmrgh..." Although, all that bubbling had used up a lot of air, and he was starting to strain. Right, time to get out of here. It's been fun, but I'd rather not drown in this thing. Swimming off the bottom, Vector punched against the balloon's edge, putting actual effort into it this time, though all that did was bulge it out. Right, right, punching kind of sucks underwater. I'll just bite the thing. With how smooth the material was, it took a few tries, but he eventually managed to get a grip on it, then chomped on it and yanked back.
PSSSHHHFFF! The balloon was successfully torn open, a massive current of water now rushing out through the rapidly-widening hole and flushing Vector out with it, letting him catch his breath. He watched the balloon deflate, and the robot's "arms" harshly curled in on themselves, seemingly not knowing they now had nothing to hold, slamming against its main body and breaking it, the whole thing falling to the ground.
If anything, Vector was actually somewhat disappointed the robot unintentionally destroyed itself. "Ah damn, could've at least let me finish the job... Never thought I'd say this about a robot, but... Man, I hope there's more of these."