The water in the pool was colored such an artificial blue that one might have thought there was a glass ceiling above it, but the room was entirely contained; a creature like the tentacled beast was far too dangerous to be let outside, and inside, it needed to be kept entertained.

Raiden was the entertainment, and after only a minute of deep, eager thrusts from the tentacle buried in his backside, he could feel the front of his tummy bulging out, as if the tentacle itself was reaching through his insides and tickling the inside of his stomach lining.

The bulge present, however, was much too large for a mere tendril to have the same impact: his normally slender torso was bowed out with such weight that he’d taken on a full, growing curve, the mass of which was still bowing out from his once narrow hips.

He could hardly believe what he was seeing, but around such a huge, stretching mouthful of tentacles, it was a strain just to open his eyes in the first place.

“Subject is displaying abnormal capacity.”

Other than the occasional, broadcasted observation, there was no more conversation to be had. Raiden had plenty he wanted to say to the research team for turning him into their sacrificial lamb, but even the grunts and groans that came with the effort of being stuffed were stifled behind the weight of the largest tendril.

His cheeks were bowed, his neck tilted, and his tongue utterly flattened by that beastly flesh...and if not for the unique properties of the substances that were flooding his body, he might have been torn asunder by the greedy beast.

“Subject also displays higher-than-normal elasticity.”

His slender form continued to bend to the whims of the tentacles, but it wasn’t just their penetration that was the cause of the same.

Even though his throat was being stretched well beyond what he ever could have imagined, Raiden felt the pressure of more than one tendril pushing against the stretched, gaping flesh of his asshole. One greedy length was hogging that entrance at the beginning, but as the minutes passed on and the jackal learned just how pliable he was, smaller tendrils pushed and nudged blindly against his backside, rubbing that flesh and taunting the jackal with the threat of even greater penetration.

Two tips pressed against his soft, yellow opening at the same time, giving his body a total of three to deal with...and as all three moved in and out of his tailhole with precise unison, they gushed a fuller helping of the messy substance that was bloating the jackal in the first place.

Colored of grape jelly and every bit as thick, Raiden wasn’t sure what the beast was filling him with, but he could see from the corner of his eye that his tummy, once thin and lithe, was blowing up as though it held a basketball inside...and that was just at the start.

His entire body was on the slim side, when he’d first entered the water. At that size, he would have had no chance to fight back against the tentacles in the first place, but even as extra girth flooded his stomach, he didn’t feel any stronger- just fuller- and those limbs were still helpless to move, courtesy of the living bondage that contained his flesh.

When the sheer quantity of the mess being stuffed into his body became more than his stomach could contain, those same arms were the first spot to take on some of the excess.

Am I actually getting bigger? Bulkier? That can’t be possible, right?

The jackal didn’t know what to make of the fact that his fingertips didn’t seem to fit into a comfortable fist, anymore. He tried to blame it on a reaction to the slick, messy gel that was flooding his body, wondering if it might be some kind of allergy...but the rest of his body was growing in time: just as he found it impossible to clench his digits into fists, he found that his toes, even with the benefit of floating in the water, couldn’t properly curl into the pads of his paws.

It was slow enough to start, given his slender nature, but once the flood of the oozy was pouring down his throat, right into his tummy and flooding him from behind, he reached his initial capacity faster than the scientists could have guessed.

What was stunning was how quickly the other parts of his body were able to pick up that slack. Toothpick legs began flooding and filling out, creating wide, thick thighs and obscuring the view of his cock in the process. Arms that remained behind him were growing round and chubby, the sinew of muscles having no chance to develop before they were completely engulfed by what looked like layers upon layers of rolling fat.

There was more jiggle to that flesh than organic cellulose, but poor Raiden wasn’t able to experiment with it all that much, trapped as he was by the ravenous bunch of tentacles.

He was stuck in that pool, seemingly alone with his thoughts...

“Subject remains comfortable. Continue the experiment as planned.”

...And a wealth of tentacles, still hidden by the surface of the water.

Those extra tendrils were already dripping with that same, oozing substance, the same being slathered into Raiden’s fur as the creature brought the jackal to a startling realization: with three tendrils buried in his ass, one larger one in this throat, and several more swirling around his inflated body, just waiting for their chance...the tentacle monster was only just beginning to show off a sample of its greed.

It was capable of far more than it had already shown, but it wasn’t alone in that regard.

Raiden worried that the pressure was already becoming too much, but as the rounded flesh of his tummy took on such tension that the flesh beneath his fur actually glistened, he felt a second and third tendril pressing at his jowls...

iOScythe was kind enough to do this YCH with my lad and it came out so good I commissioned a story from Joshiah for it! :D