Lunar excursion

With his work done for the day, a feral green dragon wandered the halls of the lunar base, somewhat bored and looking for something to do. His friends were busy, as well as most others who worked here, so the halls were mostly empty, the only sounds around being the hum of machinery and the clicking of his claws against the floor.
Passing by a window, the dragon paused to look outside. Even having been on the moon for a fairly long time by now, the sight was still somewhat surreal: A near-featureless grey expanse stretched before him, with far more stars visible than he'd seen pretty much anywhere else. This window also happened to have a view of Earth, hundreds of thousands of miles away, and a feeling of loneliness briefly came over the dragon. Just a couple more weeks until he could go home...
Looking out over the landscape, he finally decided on what to do; he'd go for a stroll outside for a while. There was a spacesuit made for him, but getting it on was a real pain, and that was if he could even requisition it for something so trivial in the first place. Although, due to a fairly recent incident, the dragon had found that he had less need for it than most.
He'd been helping transport something outside, when he'd tripped and torn his suit in an awkward spot that he couldn't manage to cover. All the air was rapidly sucked out, and, despite having previously been warned not to, the dragon instinctively held his breath. Except, instead of there being any damage to his lungs, he successfully kept in his air, with only a brief jolt of pain as the vacuum pulled at him. It had certainly been a surprise to the people monitoring the airlock, when he'd returned with puffed cheeks visible beneath his visor, followed by an exhale as air filled the room. While he'd been reprimanded for holding his breath in a vacuum, word of his ability soon got around, and he quickly became well known for it, even getting a nickname in the process.
Stepping into the airlock, the dragon pressed a button to request it to be cycled, and a voice came over the intercom. "Hey, Airtank. You're not scheduled to go out today, what's up?"
"Just going for a walk. Figured I'd try going without the suit this time, too."
"Alright, but keep in mind that there's more reason for it than just having air. The temperature might be an issue, and you'll need a shower when you come back. Can't have any moon dust getting everywhere. Sure you want to deal with those?"
"Yeah, that's fine. I think it'll be worth it."
"Okay, give me a minute..." Somewhat muffled typing was audible as whoever was at the intercom logged the dragon's departure. "By the way, there's a rumor going around that you can hold your breath for an hour. That true?"
"Not quite. An hour and a half."
"Christ, you dragons are somethin' else...Right, get ready." Just after that, a hissing was heard as the air started being pulled from the room. It was somewhat disconcerting, but the dragon kept calm and breathed heavily, each breath taking more effort than the last, until he inhaled fully and held his breath, puffing his cheeks. A second later, everything went silent, no air remaining for sound to travel through, and he lurched somewhat as the room's artificial gravity was turned off. After that, the outer door slid open, and he stepped out onto the moon's surface, his body completely bare to the vacuum all around.
As his paws touched the ground, there was a barely audible crunch of brittle stone, his own body acting as a conduit for sound, allowing it to go directly to his eardrums. He stomped, hearing a marginally louder crunch as dust was sent about a foot upwards, and watched it settle. Then, the dragon crouched down somewhat and sprung forward, launching himself a few feet off the ground and going quite a distance with just one jump. He'd always wanted to do this, but his spacesuit was too bulky to allow for it without potentially damaging something, either from the jump itself or the landing. When he reached the ground again after a few seconds, he leaped again, happily bounding along the lunar surface.
In only about 20 minutes, he'd gotten a couple miles from the base, and as he looked back to make sure it was still visible, he started getting aroused. Holding his breath tended to get him horny on its own, but being this far from any fresh air was especially appealing to him, and soon his dick was fully out of its slit and swaying between his thighs. The dragon was somewhat embarrassed at first, but quickly remembered that there was no possible way anyone would see him this far out, and felt a bit more comfortable.
Another 10 minutes of hopping, and he started to get tired from it all, discomfort finally forming in his chest. Sitting down to rest for a while, he flicked his tail back and forth and surveyed his surroundings. Still not really anything of interest, just hills, a few craters...A hole? One of the nearby hills had a small opening in it, and the dragon had to investigate. He went over to it, bouncing slightly with each step, but found that the hole was too small for him. There was clearly a cave inside, though, and he wouldn't give up that easily, starting to dig at the hole's edges to widen it. With a few minutes of work, he was satisfied with the new size, and, with some effort, managed to squeeze inside, cheeks briefly being pressed in on.
Only now that he was in the cave did the dragon notice that there wasn't actually much there, barely any more than he could see from outside. He growled in frustration, expanding his cheeks as he held in that bit of air. What a waste of time this had been. Still, it was cozy in there, and pleasantly cool as well. Deciding to at least relax for a while, the dragon sat down again, and was soon reminded of his arousal, dick now subtly throbbing.
Figuring that he still had plenty of time left before risking running out of breath, he started to awkwardly masturbate. His paws weren't really the best for this, but they worked. Some time into this, the dragon absentmindedly puffed some air from his nostrils, the pressure difference almost instantly deflating his cheeks and forcing out more air than he intended before he sealed his lungs again. Interestingly, he could actually see the air he'd exhaled, a subtle cloud in front of him that quickly dissipated. He smiled, opening his throat again and allowing the vacuum to pull more air from him, watching another cloud flow from his nostrils. Not wanting to further waste air, he decided he could continue blowing clouds of air some other time.
Eventually, he laid down on his back, his arousal building more quickly as he approached an orgasm, rubbing his dick with both front paws, and as he passed the point of no return, he stopped masturbating and actually tried to hold back his orgasm for a while. The sensation rapidly built further and further, the dragon squirming and gritting his teeth, the air in his mouth being pulled out between them. 7 seconds, he held on, until it was too much for him, arching his back and opening his mouth wide (but keeping his throat shut) as he came hard, his first shot of cum lasting a couple seconds, hitting the ceiling because of the low gravity. It was quickly followed by another, and another...For almost 30 seconds, the blissful dragon happily writhed about on the cave floor, his cock flopping and spurting cum all over, before his intense orgasm finally started to slow down. A few more weak spurts, and that was that, much of the cave walls now covered in dragon cum, its source laying contentedly on the floor, still holding his breath with puffed cheeks. The dragon was exhausted from his intense orgasm, and took some time to rest, closing his eyes...And, after a few minutes, despite not being able to breathe and it being so long since he could, he fell asleep, cheeks still puffed up.
He sleaped for about half an hour, not having any dreams. Eventually, he became somewhat restless, a purple blush slowly forming on his face as his oxygen continued running out. Soon, the dragon woke again, groggily getting up and stretching, before remembering where he was and realizing how badly he needed air. The partial breaths he'd exhaled, combined with all the exertion of his earlier orgasm, had significantly cut down on how much time he had to get back.
Puffing his cheeks much bigger, only a bit smaller than his head, he tried to squeeze back out of the cave, but his cheeks were too big to fit through. Seemingly unable to internally inhale and deflate them, he started digging at the exit like he had when he'd been trying to enter. It didn't take quite as long this time to get it big enough, and the dragon crawled back outside, quickly getting his bearings and making his way back to the lunar base. Like before, he bounded across the landscape, though certainly not enjoying himself this time. Stale air occasionally leaked from his nostrils, and while it wasn't enough to be visible, it was definitely further cutting down on how long he had.
Lungs now starting to burn, the dragon slowly got closer to the distant base, starting to get aroused again but not even considering stopping to take care of himself. His blush turned blue, his cheeks inflated slightly bigger than his head, and after a couple more minutes, he started to lose control, leaning down to cover his muzzle with his front paws. This certainly wasn't close to his record of an hour and a half, but all the exertion and air loss had reduced his limit to be just a few seconds away. As his arousal reached the tipping point just from his overly-extended breath hold, he started dry-humping and his cheeks rapidly ballooned to double their previous size. Then, at last, he stood again and arched his back, his maw shooting open.
A large, mostly-transparent cloud rapidly formed from the dragon's mouth as he exhaled, the vacuum surrounding him pulling out the air far faster than he would've been able to on his own, leaving nothing behind. At the same time, he came once again, unloading onto the lunar surface as his maw repeatedly opened and closed. He was instinctively trying harder and harder to inhale, but he knew nothing was coming, even the breath he'd exhaled already having dispersed.
Still cumming, he tried to run, his paws slipping on the dust and rocks, kicking them up along with his cum. He tried his best to focus, and leaped forward once again, not quite in the right direction but still close enough. There was still another mile to go, and while he wasn't sure if he'd make it, he'd give it everything he had. His orgasm slowed to a stop, and he jumped again as he landed, still desperately sucking on the void and shivering.
10 minutes after his exhale, the dragon neared the lunar base, as his body neared its limit. The blue blush had spread to cover most of his face and the rest of him gained a subtle purple tint, vision slowly dimming, his leaps getting smaller and shorter each time. Soon, he was essentially just walking, his maw hanging open as his body kept up its useless attempts to inhale.
Maybe about 30 feet from the base's airlock, his legs gave out, and he collapsed to the ground. He weakly tried to stand up, but couldn't focus enough to keep his paws from sliding, and as the purple tint of his body became obvious and his tongue and cock turned blue, it was clear that he was entirely spent of oxygen. With a few subtle shudders, his eyes rolled back as he...
...What kind of dragon would he be, if he gave up so easily? And so close to salvation, as well...
The dragon absolutely refused to pass out. Through sheer willpower, he forced his suffocated body to move, slowly climbing to his paws. Despite his immense determination, it was only by virtue of the low gravity that he could do anything more than twitch. Sluggishly and awkwardly, he walked toward the airlock, barely able to make out anything in front of him, and didn't immediately notice that he'd gotten into it, bumping his muzzle against the opposite door. Even that he barely noticed, but then slowly turned to what he thought was the button he'd pressed earlier, and with the absolute last of his strength, pushed his muzzle against it. Right after, he collapsed again, and, hoping he'd be safe, allowed his consciousness to finally fade...

Hours later, the dragon awoke in the infirmary with a rather terrible headache. He couldn't seem to remember anything past when he'd first collapsed, but he knew that he was going to be in major trouble for being so careless...