That boat there, a hundred feet beneath him, was once floating, Spike thought, once full of ponies, once floating and working like it was supposed to. Staring into water that under the sun took on a transluscent emerald hue, Spike pondered how such large thing could be gobbled and digested by such a calm expanse of water. Not a wave in sight, only gentle lapping curls breached the surface of the water, like fingers beckoning him down. 
The beckoning fingers of the water, in his mind, led to thoughts of Rarity beckoning him down. Rarity, with her amethyst threads of hair spreading out like an angel’s wings, curtaining her face like he was watching her perform a striptease. Rarity, with her perfectly proportioned breasts floating, cushioning his face. Rarity, with her arms drawing him into an embrace that would last forever, with her hand smacking his cheek over and over and yelling his name–
“Spike!” 
The small dragon yelped, wiped a bit of drool from the corner of this lips, and turned his face as the hand on his stinging cheek pushed him, coaxed him to look up. The figure in front of him was not Rarity – because of course it wasn’t. Spike would have done anything to get Rarity alone with him on this yacht out in the middle of the ocean. Just him and her, bobbing up and down softly, relaxing on this boat as Spike caressed her amethyst locks.
Instead of amethyst locks, this pony had amethyst curves, powerful thighs sculpted and polished, fit for an art museum. Her stomach gave an hourglass-curve inward before her silhouette rounded. Spike stared slightly at the twins she was dangling practically into his face, round and soft with dark rings in the center. 
“Ah!” Spike fell back in slight surprise, then stared up into the face of Twilight Sparkle.
 She brushed hair the shade of foggy evening out of her eyes slightly, and one strip of pink like the dawn horizon fell back slightly before she pushed again, more insistently. “Did you hear me? I’m ready to go. We should get going before noon. I’ve read this part of the sea can be unpredictable! In fact, in Saltimus Ahab’s Seafarer’s Almanac, I read–
“Ok, I get it!” He looked down and muttered. “You didn’t tell me you’d be naked…”
She giggled slightly. “Oh Spike.” She patted his head slightly. Standing, he came up to about thigh-height, so sitting on his butt like he was, he barely came up to her knees. “I told you this yesterday! Clothes slow you down! I suppose I could have maybe gotten a nice skin-tight wetsuit, and in fact I was debating it, the Diver’s Guide To Apparrel made some convicing arguments for both nude diving and for skinsuit diving so–
“Twi.” Spike pouted. 
She giggled again and moved toward the edge of the small yacht, peering down into the water. “Don’t complain! Don’t forget, you’re naked too!”
“I’m always naked, that’s different” he muttered. Upon saying this, he subconsciously covered his dignity. It was still, shall we say, “awake” after daydreaming about Rarity. And that’s the only reason it was! For sure. Spike patted his flushed cheeks and looked up at Twilight, up at the soft, supple curve of he behind as her tail swished side-to-side in excitment. 
She’s basically like my sister, he thought. And besides, she’s… Well, not Rarity! 
With a rough shake of his head, as if he was trying to knock a drop of water out of his ears – or  in this case, a thought he didn’t want – he took a deep breath, then another, his green-plated chest rising and falling with almost dramatic intensity as he flooded his lungs with oxygen like she had taught him. Bla bla bla, Dumb Stupid Book About Swimmy Stuff said that you’re supposed to take several deep breaths before you take the one you hold. “There, am I doing this righ–
Splash. Where Twilight had been was nothing, and in the water off the side was a set of concentric ripples, a burp of white foam from the sea, and a shimmering form of Twilight as she descended. It was like looking at Twiglight through the lens of a long-forgotten memory, or a dream from which he was about to wake. 
She was already going! She always did get excited about books, Spike thought. He hadn’t really been paying attention the previous night as they had dined at the pub back at port, but she had nerded out to him about the hundreds of rare, nay, one-of-a-kind books that they might recover. Spike wasn’t sure how she planned to get any use out of waterlogged books, but then again, he’d spent the whole dinner wishing he’d stayed home with Rarity. 
Now Twi was leaving him behind. So, with one last deep breath, he leapt to meet the beckoning fingers of the sea, breaching the foam and entering a world that felt upside-down, weightless, like the moon’s embrace. All color shone weakly through a film of marine greenish-blue. All space seemed distorted as if seen through someone else’s glasses. And there beneath him, thighs, biceps, feet, and hands chruning like gears in some great machine, driving it forward, was Twilight Sparkle.
“Mmglrp!” Spike let out an involuntary gurgle as his something between his legs stiffened. It wasn’t his tail. The form below him, hair swirling like a halo above its head, thighs and buttocks pushing, churning, jiggling slightly in the salty brine, breasts wobbling softly and bouncing together… A poet could have filled tomes, volumes with what feelings such a sight might evoke, a songwriter could weep tears of desire and anguish and attmept to transcribe the sound as a chord of sheer lust and unearthly hunger. Spike, a small dragon boy who barely came up to this goddesses thigh, a small dragon boy with a shameful boner and rosy cheeks, could only muster one thought, using the most eloquent words he knew. 
Holy shit. 
Twilight would kill him if she even knew he thought with such language, but Celestia damn, he couldn’t help it! Perhaps it was just a property of the water, but Twi, who looked so plain to him above the water, who looked like a complete book-kissing nerd, who reminded him of work and chores and how inadequate he was intellectually… Down here, she was entirely transformed, like an ugly duckling turned swan. 
“Glglg…” He gurgled. Air! He cupped his palms to his lips as his cheeks bulged out suddenly, sending a stormcloud of bubbles upward to the world beyond the surface. He swam up, gasped, gasped again, and smacked his cheeks. This caused him to sink a little, and he had to use his arms to help him tread water. “Hold it together, Spike! We haven’t even made it down there yet!” 
Then, like a mermare breeching water, Twilight ascended beside him, arching her back and gasping, sending her hair in a perfect arc upward, drawing a semicircle with droplets of water along her hairtips, and settling into a gentle tread upon the water’s surface, hair wet and slicked back. 
“I’m sorry Spike!” She giggled. “I got so excited I didn’t signal I was ready to go!” 
Nerd. Spike huffed, his sudden and strange excitement subsiding. It was just Twilight. Just boring, stick-up-her-ass Twilight, virgin queen of the books. Nothing special. Certainly not Rarity. He tried to think of Rarity being in front of him instead. Amethyst locks, pearl fur, seductive eyes, cute, dorky grin, purple lips–
No, those last things were Twi. What the hell was going on?!
“Spike?” She gave his cheek a soft smack. “Stop thinking of Rarity!”
He pouted. “I’m not.” And for once, he was telling the truth. “Let’s just go.”
“Don’t be moody!” She nudged him teasingly. “I’m gonna need your help down there, not a tantrum, ok?”
For some reason, her nudging him teasingly like this set something in him afire. “Don’t treat me like I’m five, Twi!” He suddenly didn’t want her to see him as an inferior, as small, as weak. But why?
She giggled. “Alright, alright.” She looked down into the water. “You know, I read it was 100 feet, but 100 feet is a lot further down than I was expecting. I can’t tell if the water is obfuscating the real distance or if the physical reality of the situation is just more than I bargained for.”
“Ob…Fus…” Spike blinked and worked his mouth around the big word. Twi had a habit of using words that he was convinced she made up. 
“Obfuscate.” She smiled. “It means to– 
“I know what it means!” He said, obfuscating the fact that he did not, in fact, know what it meant. “So… Does that mean we’re going back?”
“Nope! Just means a slight change of plans. You’ll swim too slow to make it down there before you run out of air.” She huffed out a little breath, as if to demonstrate running out of breath.
He pouted. On the one hand, he didn’t like being infantilized – one of those big words that Twilight sometimes used, one whose meaning he knew all too well. On the other hand… “Does that mean I go back to the ship?”
“Nah! Give me a moment to get a few breaths, and then get on my back.”
He blinked as she breathed deeply, her chest expanding and contracting as she took breath after breath. He stared down at the water so he didn’t stare at the heaving of her breasts. And so she didn’t see the shade of his cheeks. “On… Your back?” 
She smirked. “’Back’ is the part of your body that’s behind you–
“I-I know what back means!” He pouted and swam over to her. This was ridiculous. Was he really going to get a piggy-back swim ride from Twilight like he was a baby? Sure he was small, but this was just humiliating. “Never, EVER tell Rarity about this. Tell her I swam on my own.”
“I will.” She giggled, took a few more breaths, and nodded to him. He wrapped his arms around her shoulders and pulled himself to her.
And he froze. Not from the temperature of the water, which was admittedly rather chilly, but from warmth. Sheer warmth and softness. There was something almost motherly about Twi as he clung to her back, something comforting. A strange mix of love for his sister, admiration of the muscles he could clearly feel along her shoulders and back, a sort of nostalgia for when he was a baby and she would sing to him, and some ingredient he couldn’t name fermented in his stomach, and he felt drunk off of it. He pulled himself closer, face almost burying in her neck, resting his member against her lower back, and just holding her. For a moment, he didn’t even care if they went under, or back to the boat, or just sat here until moonrise.
“Spike?”
“Hmmm…?” He sighed.
“Deep breaths, remember?” 
He blinked, pulled his cock a bit away from her back, and swallowed hard. “R-right…” He shook his head, let out a puff of air, and let out a laugh that was far too loud. “I guess I got distracted. You know. Thinking of Rarity!”
Twi blinked at him as he breathed in and out with frantic energy, his chest pressing against her back with each breath. And with each press of his chest against her, he couldn’t help but imagine he was holding onto cloud, or a soft blanket, or a strong and powerful dragon mother. He blinked a little at this last thought. Damn me, he thought. For one, why was he thinking of who his mother might have been? He hadn’t done that in years. And second, he had not five minutes before been staring at this voluptuous, soft, well-endowed woman the same way he looked at Rarity. He couldn’t be thinking of her both like a mother and an attractive mare. That was just wrong!
He took one more breath, pushing these thoughts from his mind and gripping onto Twi’s shoulders instead. With a puffy-cheeked nod, she gave a grin, held her own breath, and soon they were beneath the lapping surface of the sea, down amongst the cold and salt, down among the green-tinted world. 
Even with eyes blurred, Spike could see their target far below them. Damn, she hadn’t been kidding, that ship may as well have been in another universe. Its shattered mast, scattered deck, and broken hull looked like some long-forsaken dinosaur skull, porous and half-decayed beneath layers of embalming sea. Though the ship surely hadn’t moved since it sank – when had Twilight said it was, a hundred years ago? – its silhouette held a spooky potential energy, like it might suddenly open its terrible jaws and swallow them down. Spike’s heart began to pound faster. As they sank, the green sun-tint of the sea around them began to fade, as if the sunlight that had dove with them and lit their path was beginning to slow, grow sluggish, as if it wished to sleep rather than continue with them. The ship wasn’t that deep all things considered, but the darkening of the shadowed sea around them made Spike feel like they had descended down beyond where any mammal life should be, down to places where oxygen was a myth invented by eldritch seadwellers to scare children, where uninvited guests found themselves to be permanent residents. He gripped her shoulder like a child being led through an unfamiliar town, trusting her, not wanting to lose her.
She, meanwhile, began to swim faster. The casual looseness in her shoulders betrayed an almost playful excitement. She didn’t see the dark waters and the horrible ship, didn’t imagine the depths digesting them forever, but instead thought of those damn books, he could tell. He could feel her tail wagging, feel her tail brush against his foot. 
Damn nerd. And yet… Comfy nerd. He pulled himself closer, burbling against her back. Were he able to speak, he’d make a sarcastic comment like “gee, I sure hope you know what you’re doing Twilight, because we’re going pretty deep, and there’s no air down here–
An inward kick, a message from his chest. “Whoa buddy,” it seemed to say, “glad you’re having fun, but you’re forgetting something!” And indeed he had forgotten. 
“Mmbl…” That feeling of descending into an endless throat sank into him just as surely as they sank into the sea. And it was at that moment that Spike realized that he actually didn’t know her plan from this point. Was he supposed to hold his breath for this whole journey? Did she expect him to be able to do that? She had gone over her plan in obsessive detail in the pub the night before, complete with maps and charts and a Celestia damned research paper (because of course she did, the nerd). What had she said? 
“Mmm!!” With a small glob of CO2 bursting from his lips, escaping his overfull cheeks, he shook her shoulder as if to say ‘ok Twi, that’s enough, books aren’t worth this!’ Any moment now, he knew she would turn to him, grip her in her arms and cradle him to her chest – her nice and soft and warm chest DAMN IT SPIKE STOP THINKING OF THAT – and take him up to the surface. Easy as that. 
Any moment now. 
Their descent continued with redoubled speed. Any moment. The water was getting darker, or was that just the tunneling around the edges of Spike’s vision? His limbs were shaking, and was he losing sensation in the tips of his fingers and toes? He couldn’t stop shaking. “Blrp.” Another small cloud of air pointed the way Spike wanted to go, up, up damn it! Up with the bubbles, up to the lighter sea, away from the dark stomach, away from the ship, to air!
 His chest gave another kick. “Ok,” it said.
“NOW, SPIKE!” Spike obeyed his neolithic instincts, instincts that existed long before he was born and would continue long after he passed onto the next world – and if he didn’t obey them, he’d be passing on far sooner than he’d like. His claws dug into Twi’s shoulders, and he pulled, trying to steer her like, well, a horse, using her shoulders in lieu of reins. He tugged, trying to force her to go up, up. His lips pursed, and unearthly colors danced in the corners of his eyes. The CO2 in his cheeks, like prisoners of this war against drowning, begged to be released, begged to go up just like he did, but someone had to go down in this war, someone had to sink. “M-mm…” He felt dizzy, chest pushing in and out faster and faster, legs kicking, and he pulled. 
“A-aghblglgl!” Twilight gargled in surprise as he gripped her, as he tugged. “Spiblke!! Nobl!!” Then she tried to pull him off her shoulders. 
Wait. Why was she doing this?! “Mmmm, mmm!!” Spike shook his head, tried to hold on, but she managed to pry him off her back. No, no, she was leaving him! Why was she leaving him? First color, then darkness overtook his vision as his eyes began to roll up, as his lips relaxed, just a little, and as his limbs gave one last jerk. 
Then he opened his mouth, and he could feel it rushing in. He could feel it, warm and soothing and… Soft? Was this drowning? This wasn’t so bad. Something warm linked with his tongue. Something warm pressed against his mouth. Was this death? As morbid as it sounded, Spike couldn’t help but wonder why he hadn’t done this sooner. The water was so much warmer, sweeter, softer than he expected. 
Yes. More. He sucked in greedily, felt something vibrate his lips, a sound almost like a moan traveling through him, and he could feel death pulling away from him, or trying. Spike’s chest stopped convulsing, and in fact went calm, moving up with proper rhythm to keep the machinery of his body going just a little longer. “Air, Spike,” his chest seemed to say. “I have air.”
Spike opened his eyes. And what he saw was not death, not heaven, not salt-encrusted sea spirit, but a pair of deep purple eyes, eyes staring so close, eyes sparking with frantic adrenaline, sparking so violently it seemed like a flame may erupt in the space between Spike and these eyes.
The small space. Barely any space.
That soft feeling on his mouth… That coil of flesh linked with his tongue… That sweet flavor… 
The dragon boy pulled away in a sudden panicked frenzy. “Twiblblighbl–
She covered his mouth then and gave a stern expression, and in the details of her face, Spike could see three facts.
One, she had saved him. Of course she had. She had shared the very air from her breast and given it to him. Why had he ever doubted her?
Two, she wasn’t mad at him for tugging on her like he had. She’d been worried, and now was relieved that her little Spike was ok.
And three… 
She was almost out of air.
Spike froze for a moment in indecision, and far more horrifying, she seemed to do the same, her legs kicking not with the graceful efficiency she’d been exercising before, but with nervous energy as she floated in front of him. She seemed to be deciding something, and Spike had a very strong feeling it was something he didn’t want to consider. Her chest kicked inward, and she let out an audible “arblblbl,” and Spike winced. Her chest, he knew, must be burning, much like his had been. 
“It’s your fault darling,” said Spike’s inner voice. His inner voice, of course, sounded like Rarity. It only came out when he needed it most, and right now he REALLY needed it. More than ever. “You should have trusted her. Now look into her eyes. She’s thinking of just giving you the rest of what she’s got. She’s thinking of telling you to leave her here, just to be sure you make it back to air.” Spike’s eyes widened. “She could surely make it on her own. And she might even be able to get there with you. But she isn’t willing to risk that with you when you clearly didn’t even pay attention to her, didn’t even want to come. She won’t let you die on a trip she dragged you on, Spikey Wikey…”
 No way. And yet, Twi moved close to him again, the warmth of her lips piercing the veil of water that separated them, as if she were bride and he were groom and he pulled back her wedding veil to kiss her. It was an odd thought to have so deep, with so much on the line, but he couldn’t get the image out of his head. He tried to pull away, tried to lead her downward – the ship was so close, he could see it as he looked down! – but she gripped his cheeks and moved in for the kill. The kill of herself. 
Spike didn’t think when put under pressure. Like all dragons, Spike had the disposition of a bomb under stress, and he exploded. So he smacked her cheek. It made a flat, water-dampened sound, a sound so small and insignificant it almost wasn’t there. And yet the muscular purple mare pulled back in surprise, eyes wide.
“Good, darling. Now, do you remember what she said last night? Focus. Remember. What was the plan, Spike…?” At the coaxing of the imaginary Rarity in his mind, he thought. And in the silence of the water, surrounded by nothing but his big sister, the wreck she wished to plunder, and his own mind, he remembered. 
“I did a couple of preliminary dives already, Spike,” Twilight had said. “I didn’t get very far into the ship, but right inside the starboard side – that’s the right-hand side, Spike – there’s–
That was all Spike needed to remember. He gripped the mare’s hand and guided her downward, not so much pulling her as he was encouraging her. She did all the work. Seeing what he was doing, her legs revved up and began to kick, her arms began to pull her through the water as if she was climbing it, gripping it, and her face, blue-tinged and cheek-round and sickly as it was, held a spark of determination. 
A large bloosh of air left her nostrils, and Spike urged her to go, go faster, ignoring the childish whines of his own chest, a chest with far more air than that of his sister. Her air. Twi’s air. Twi was a part of him right now, closer than Rarity ever had been. So even as they swam through the gaping jaw in the ship’s starboard side, even as they dove in amongst its guts, forgotten hallways and rooms like the steel intestines of some steamwork beast, Spike didn’t feel afraid anymore. 
Come on, Twilight, he thought. You know where to go. 
He could sense she could, as her hand tightened its grip of his, an unbreakable chain between the two of them, and she shot ahead, now pulling him. 
“Glrgl…” She let out a gutteral, deep sound, the sound of a slowly dying animal rather than of an intelligent woman, the sound of something dumb and primordial, instincts from beyond the start of history. 
The he saw it, the slightest shimmer ahead of them, a shimmer that could only be caused by the change of mediums, the change from sea to salty air. Yes. This was it. They had made it. He didn’t even realize he had pulled ahead of his sister again. Not until the supposed unbreakable chain of her fingers intertwined with his loosened. 
“Glk…” 
Spike turned just in time to see it. An animal where his sister had been moments before. Twi was a gorgeous, strong, chiseled thing with her hair always neat, her eyes sharp and brimming with the knowledge of a thousand books. The animal he regarded now was pale, kicking, thrashing, jaw agape as if in the throes of puking, hair a tangled mess swirling in front of eyes spiderwebbed with veins, tongue outstretched in waterlogged agony. 
He let out a scream he couldn’t hear over the hiss of air leaving his throat. 
Spike the Dragon was a small dragon boy. Small. He always relied on others. It was so easy for both himself and others to forget that he belonged to what was perhaps the most powerful race in Equestria. Small, harmless, gentle, helpless. That was Spike. 
Just as his sister had transformed into a dying mammal, a slouching, sucking beast, Spike heard the call of his ancestors. For a moment, he changed. He kicked hard, kicked toward her with powerful, measured strokes. One arm slipped around her waist, pulled her close to him, held her to his chest, a chest brimming with dragonsfire, with strength, with confidence. 
And then the dragon brought the damsel to the glimmer, to the pocket. 
Spike gasped. The mare coughed harshly, coughing up a half-lung of water. And in that moment, Spike became Spike again, Twilight became Twilight again.
He knew this because he started to cry into her chest.
“Sssh… S-Spike…” Twilight said, voice hoarse, ravaged by water. “Sssh… It’s ok, Spike… You made me so proud…” 
He couldn’t stop crying. He clung to her, shaking, whimpering, heart pounding and threatening to escape his chest, as if to escape, too late, the fear and heartache he’d just endured. 
“Spike…” She petted his head softly, stroking his spines in a way she knew always calmed him down. “…Those books… They can wait. We can go back up after that…”
Spike breathed deeply of her scent, nose pressed between her breasts, his whole being surrounded by her essence. For a moment, he thought of holding a mare, of kissing her, of being hers, of her calling her his. And it wasn’t Rarity he thought of. 
“…No.” He said, looking up at her, sniffling, wiping tears from his eyes. “We’re getting those books, nerd…” He kissed her cheek, then began to take deep breaths again, preparing himself for the journey to come.