“Ready to proceed, Colin,” Gavin’s voice came on the speaker, echoing in the chamber of the tank. I didn’t miss the exasperation in his tone. It made my chuckle. 

I smiled up at him with that shit-eating grin I’d been wearing ever since the transformation more than a month ago. It was no secret how much I’d loved it, though my coworkers didn’t comment much on the subject. I know they had borne witness to my very lewd displays, and I had it under good authority that some had shamed me for it, though not out loud. Fuck them. If they had felt what I felt, seen what I’d seen, the entire base would have touched themselves just as much as I had. Hell, I bet some of the more prudish employees would have done much worse! 

My supervisors didn’t want me on the next assignment, no surprise there. I’d acted unprofessionally, they’d stated. Despite reports from similar labs that indicated heightened arousal from such a nanite transformation was common. I’d apologized as profusely, and I must admit, as fakely as I could. I was fearful that I wouldn’t be allowed to change again. But, much to my excitement, no one wanted to take on the next project. I was the only one who had put my name forward. Buncha cowards! 

So here I was, in the chamber, naked this time, awaiting my next change. I could see why this tech was currently banned for requiational use. It was addictive! I couldn’t wait to feel the rush of change, especially in my cock.

This time I was to be something with gills. Once again it was something at the top of the food chain, to minimize risk to myself once I was out there. Again, it was a test run, seeing the limits of a new body. But this time, I was expected to be out there over a week! 

I wasn’t allowed to pick the form, not after the last debacle, but with some carefully slipped bills I was granted access to the parameters that the change would grant me. I’d be a shark regardless, but choosing what kind of shark I was to be was key. I’d always had a personal favor towards tiger sharks. That, and I wanted to add some personal modifications I thought suited my form rather fetchingly. 

I was especially excited for the body that would soon be mine. I knew sharks had a split or hemi penis and I couldn’t wait to feel what that would be like. I wanted some muscle mass of course, but not too much. I didn’t wanna give away how obvious it was that I’d had a hand in choosing my change. As much as I’d fantasized about street sharks well into my adult life, I found their forms too bulky for my taste. I wanted something a little more streamlined, especially for swimming or hunting prey. 

Lost in my thoughts, I was almost unaware of the change playing over me. As before, the changes started in my tailbone. I felt that familiar ache in my backside as my tail started pushing out. It was so crucial to my new physiology. It was the thing that would steer me through the water and allow me to hunt,and explore. It didn’t hurt; nothing that the nanites did was especially painful. It felt strange though, feeling my spine extend out above my ass. It swelled with flesh and muscle, a pinkish strange-looking thing sticking out the back of me. 

I watched as the tip of my tail tapered to a point, splitting at the end while one end grew slightly faster than the other.. A light tingling informed me that smaller fins were growing off the sides of the larger one for aid in swimming. As before, I had to hunch over a bit as my tail began touching the floor. It would get fairly long, I figured. I hoped the chamber would fill up with enough water to let me swim.

I was becoming a variant of a tiger shark this time, only I’d taken some… creative liberties with the form. Those started with the change in coloration. Tiger sharks ranged a variety of colors between bluish grey and brown. But as I watched my hands, I could see a patch of orange flesh spreading along the backs and slowly moving up my arms. Pale white skin spread up on my chest and towards my neck. 

I could feel the skin begin to tingle, and I longed to touch it, but remembered that was a bad idea. I knew my skin was being covered slowly with thousands of tiny denticles, or little teeth. If I accidentally rubbed them the wrong way, they’d cause me to bleed. I was sure the nanites would fix the skin damage rather quickly but that wasn’t the point. I didn’t know how powerful the shark’s instincts would be. A single drop of blood in the water, even my own, might make me go into a frenzy, and make it impossible for me to leave the tank. 

As I watched the sharkskin spreading over my chest, down my legs, and towards my still- growing tail, I could see the beginnings of firm muscles taking place on my normally lithe form. My pecs were beginning to flatten and bulge, stitching out my chest. My stomach was tightening up, the start of a six-pack forming, giving me abs the likes of which I had never dreamed of. My biceps and deltoids were springing up with firm muscle, making any gym work pointless. I was ripped as fuck!

I couldn’t help but feel my cock start to stir at the sight of my increasingly-sexy body. I would have blushed in embarrassment if the orange skin hadn’t made its way up past my cheeks by that point. That, and everyone had already seen my play with myself last time. 

“Don’t get too excited Colin. Everyone’s watching, remember,” Gavin said, clearly aware of the slight bulge my member was sporting. 

I couldn’t really hide it, not with all the cameras watching and nude as I was. But that was OK. So long as I didn’t touch it, or at least held off as long as I could. But, given the sight of my sexy, increasingly-muscled form in the mirror, I wasn’t sure how long I’d hold out. 

I felt itching on my body as all my hair began to fall away. It dissolved before hitting the water that had just now begun to splash up around my still-human feet. I shivered from the contact with the cool liquid. But I knew it wouldn’t be too long before I was comfortable in my new environment. I felt the same tingling on my head, seeing my medium-length blond hair fall away around me. I took in my bald head as the orange skin moved up the back of my skull, admiring the sight. The muscled visage and bald head really suited me!

I felt my legs tingle as they began to lengthen, and I stood up straight for a moment, alleviating the cramping from my back. I knew this would be a non-issue in a few minutes. The water would fill the tank enough for me to lay vertically and swim out to sea. The relief was welcome nonetheless. 

I could feel the tingling centering in my toes. I looked down to witness a change that reminded me of the orca form I’d taken on a little over a month ago. My large toe and little toe retracted into my foot as my remaining three digits extended. A fine layer of webbing ran between the toes as the orange skin slowly spread towards my expanding feet. I felt a poking sensation from the back of my heel and watched as the remnants of a fin sprouted there as well. I wasn’t sure of its purpose in my new body. Perhaps it was some semblance of shark anatomy reflected in the hybrid form, but I wasn’t complaining. It kinda looked cool, at least. 

I watched the white skin on my belly spread while orange overtook the rest of my form. Black lines began to take shape, getting me hard all over again. I had the signature stripes that gave the tiger its name. Though normal tiger sharks weren’t orange. It was a terrible color for camouflage. But I wasn’t worried about that. I would be faster, smarter than any other predator in the ocean. It wouldn’t matter if my prey could see my coming or not. I shuddered in joy as the black stripes crawled over my skin, accenting the orange and white coloration well. 

My hands began to tingle next, as did my elbows. I could feel the webbed skin stretching on my elbow, the remnants of another set of fins I was to have as a shark. And I was fairly sure that they’d help me steer. Like my prior orca change, my fingers stretched longer, pointy like claws, but not as sharp. I still retained three fingers and a thumb; the pinky retreated into my wrists as the remaining digits stretched further and filled in with a fine layer of webbing between each, fit for smooth swimming through the waves. 

I looked down at the familiar sensation of my biceps expanding, bulking up with muscles and strength needed for pulling my body through the ocean. I felt my cock leak all over again. I loved the sight of bulking up, adding on pound after layer of muscle effortlessly. I’d tried hitting the gym after I returned to human form the first time, but the effect just wasn’t the same. I could never achieve the sexy muscled bod I craved without the help of the nanites, and I was thankful they were allowing me to bulk up now. 

I suddenly felt my jaw ache, and I moved forward, almost losing my balance and hitting the steadily rising water. It was up to my knees by now, though my legs were still stretching a little. I felt my jaw crack and expand. My mouth opened further into a menacing grin as my teeth itched and more rows sprang up in my maw. I could taste the blood as new serrated teeth grew up in rows behind my human teeth, which themselves were thickening and sharpening into points. My mouth grew wider into a dangerous grin to accommodate the increased number of dentures. 

I watched in the mirror as my eyes widened and grew into golden slits, the fierce eyes of a predator. My nose expanded towards a point, but then closed, leaving me only able to breathe through my mouth. A strange ache erupted on my head, something bubbling up from the skin like a flap of some kind. I was growing a crest, one longer and pointed like the thin flaps of webbing that lay between my fingers and toes. I pondered its purpose; it wasn’t my dorsal fin, was it? No, I could feel a tingling lower on my back signaled my dorsal fin protruding. Maybe it was a second fin for steering in the water. I would find out soon enough, I supposed. 

The tingling soon centered in my already erect cock, and I knew what was coming. My cock was hard already, but the sudden surge in my member left me boned. It was getting longer, the skin turning dark, almost grey, a stark contrast to my orange-white skin. I shivered from pleasure as my cock head tapered and the foreskin pulled away, exposing the thickening flesh. 

Then the moment I was waiting for finally came. A sensation emanated from the widening tip as the pointed end began to cave in on itself and the edges began to slowly peel away like a banana. I gasped at the alien sensation. My cock split slowly down the middle, each half thickening and fattening into two distinct members, each larger than my human penis had been! I longed to touch them. I could see them leaking out of their tips as the ridges and veins bulged out. Right away I felt my balls swell before slowly entering my body, to be protected in the streamlined form I would wear once the transformation completed. 

My body continued to swell out with muscle. My biceps and deltoids bulging, my ripped abs a perfect six pack, my leg muscles firm and rigid. Once again I was swelling with bulk, putting on pounds and pounds of raw muscle. That realization made my cock throb a little more each inch I swelled. I was the epitome of any bodybuilder’s dream, a muscled Adios. I bet I could easily bench more than the world record. That is if I could remain on land long enough to do so. 

The moment that I had feared most had arrived. I felt my neck tingle and open up with a series of slits appearing across the flesh of my neck and beating furiously. I couldn’t breathe! Wait, no, that wasn’t quite right, I could breathe, at least a little. My lungs had not collapsed yet, but I felt a bit weaker. The air entering my lungs through my mouth was insufficient to meet my metabolic needs for very long. The water was up to my waist by now, and I considered diving in, but I wanted the change to complete first. Plus, the hatch to the opening hadn’t opened yet, so I had nowhere to go. 

I couldn’t hold back. I didn’t want to. I was feeling a little out of breath, and I needed to touch myself before diving into the ocean water. It was a primal need, bestial in its intensity. The swelling of my muscles, the power in my new form, feeling my expanding jaw, the tingles running through my body. I couldn’t imagine not giving in to the pleasures of my new flesh. My webbed hand rubbed gently over the base of my bulging grey cock, a shiver of pleasure running through my very being. 

“Colin, don’t-” A voice said before cutting out. That break was all I needed. I couldn’t hear him, after all, so I had no idea what he’d said. 

I chuckled over the technicality as I grasped my twin cocks tightly. My one webbed hand, though massive, hardly sufficient to get around both of my thickening members. I took one cock in each hand, feeling the space between them expand as they both grew to massive proportions from just the slight contact. My body was still weakened a little from the lack of oxygen but from the way I was feeling, this wasn’t gonna last long. 

I could sense a churning from inside me, a powerful surge of pleasure shooting into my groin where I knew my former balls had retreated into. They were bulbous, protected, massive. I took a webbed hand from my cock for a moment, rubbing the perineal area underneath my cock, just above my asshole. There was a slit there for my cocks to retract into when not in use. Even the gentlest brush of my webbed flesh was enough to send me into sensory overload. I alternated between rubbing each thick, gray pointed cock while pleasing the skin just above my balls. I reveled the feeling of them swell inside me with the rich orgasmic release they would soon bring. 

I continued to bulk up, not as large as the monstrosities from street sharks, thankfully, but enough. The sexy visage in the mirror gave me all the encouragement I needed to touch myself and fuel the growing lusts from my twin cocks. The changes were coming to a close once again. Although I wasn’t the size of the orca I’d been, it was enough. I was over 7 feet tall, thick and muscled. I still held an athletic build, like the swimmer I was meant to be. My tail waved behind me as the water rose, adding to my overall length. 

It was coming. I couldn’t hold back, didn’t want to. I needed to cum. The powerful cramps shooting through my groin and prostate were insistent as I rubbed my tingling organs with increased reverence. I took both of my cocks now, one in each hand, as I prepared for the release I so desperately craved. Ever since my experience as an orca. Ever since I’d last touched that magnificent cock. It was so close, I couldn’t hold it back… 

I stood there with my mouth agape as both of my cocks shot torrents of seed into the frigid water. One pumped after the other, twin cannons of shark flesh that made my body cry out with waves of orgasmic release. It was almost too much; my vision whited out and I nearly fell forward into the water. I managed to keep my footing as the water flowed up past my cocks. The cool saltwater was refreshing as my body fell into post-orgasmic bliss. 

Satisfied with my orgasm, I dove into the water, a powerful surge of energy flowing through me as my gill slits flicked and I was finally able to breathe properly. I felt so powerful, so free, far faster than the orca as I tore my way through the water and out into the open ocean. I was home once more. 

******

Being part shark was in many ways so different from the orca body I’d worn not a month ago. I was faster, sleeker, more streamlined than before. None of my prey was a match for my speed. I fed well, tearing into fish of all sizes and shapes to satiate my hunger. There was a wide variety of species in the trenches that I did not recognize and unfortunately could not report on as they quickly became my lunch. But the nanites took care of the DNA analysis of whatever I was eating.  

Living underwater was an amazing experience. I couldn’t go too deep; there were points where the pressure was too great, and areas where I could not see. My vision was decent though the range left something to be desired. But my sense of smell more than made up for it.  It quickly became a game I played, chasing down scents that even the shark brain cared little about.

And then of course there was the blood. It really was true what they said about sharks and their ability to smell a drop of blood in gallons of water! My nose scented the water at all times for that delicious metallic tangy flavor that sent my senses into overdrive. I craved the scent, went nearly mad over it. I found the flavor of wounded prey so much more fulfilling than other prey items. 

I explored deeper, further, farther than I had before, gathering the vital data my company needed simply by swimming. I did tire occasionally; in those times I felt my brain shut down as my body kept moving of its own accord. My body kept needing to move to keep the necessary water flowing into my gills. I could breathe in the air to some degree, but I didn’t really see the need. There was nothing up there that caught either my own human needs or my sharkish desires.

I possessed a new, strange sense, an awareness of currents and beings around me that I had not experienced as an orca. My partially shark brain was aware of how to use it, which was a relief, as I had no clue. My lateral line, tied into the earth’s magnetic field, allowed me to pick up signals from other fish. It was a fascinating sensation, one that gave me a wider range of awareness of the world around me. It was wondrous in a way no human could ever really understand. 

Finally, and best of all, my sexual desire was heightened even from my time as an orca. Having two throbbing members that reached erection at a moment’s notice. That constantly craved attention, desirous to be touched, rubbed. It was absolutely sublime. I longed for a way to stimulate both cocks at the same time while rubbing the sensitive flesh behind them where my balls now lay. But I had to settle for alternating between all my areas of sensitive flesh. 

It was an amazing feeling, my powerful tail propelling me forward while stroking my twin cocks. I was shooting jet after jet of thick seed behind me, coating the ocean water in my lust. I needed constant stimulation. Whenever I wasn’t eating or resting my throbbing cocks demanded attention. Even when my balls were dry and orgasmic release took some time my cocks were never sore or chafed. Never before had I fathomed such sexual stimulation!

******

The vibrations of a helicopter one afternoon reminded me that my time was up in this form. They were able to track me through the nanites, if I recalled correctly. I reluctantly swam back along the familiar channels toward the lab. I needed to be human again, after all. The nanties experience could not be permanent, as much as I longed it to be so. 

I was so tempted to touch myself one final time, but I was spent from the frequent sessions. Not to mention, I didn’t need to be in more trouble than I already was for having disobeyed protocol and staying out past the allotted time. Still, I would always remember the sexy form I’d worn on this particular excursion. The thoughts of my time at sea made my twin shafts rise once again, for perhaps the final time. Fuck it. Touching my twin throbbing cocks once more before entering the chamber and changing back wouldn’t hurt, right?