That's What You Get for Sleeping in the Nude
by GlaringEye
See https://www.deviantart.com/glaringeye/art/That-s-What-You-Get-for-Sleeping-in-the-Nude-GIF-1364443252 for an animated gif illustrating this story.
Matt had always been a little self-conscious about his preference for sleeping in the nude. He hated the restrictive feeling of sleepwear tightly tangling on his skin, but had been discouraged from indulging by his parents. He was particularly scarred by a VERY awkward conversation when he was growing up in Santa Cruz in which his mother had warned him that he should wear pajamas so that "if there's an earthquake you won't be running through the streets naked."
Matt had dismissed her concerns, but now as he was literally running naked down a dark alley in San Francisco, he did question his decision not to wear pajamas--especially since they might have provided some protection against embarrassment and cold... and maybe even the clammy cephalopod that was now writhing across his bare skin.
Speaking of the cephalopod, he now realized it had been a huge mistake to purchase it. Matt's massive aquarium was his pride and joy...and the beneficiary of a shocking percentage of his salary and free time. Even though the online reviews for the cephalopod were spectacularly positive and the documentation said the cephalopod was definitely compatible with all of the fish he owned and acclimated quickly, things had started changing immediately after he introduced the new creature into the tank.
Some of the changes were positive. For example, Matt had initially been delighted with its cuttlefish-like ability to vary its coloration, which he found mesmerizingly beautiful. Before long, he had found himself staring at the tank for hours enjoying its complex movements and patterns.
Occasionally, he would be confused at the increasing shyness of his other fish, but those thoughts didn't linger once his attention was once again captured by the cephalopod. As it grew and grew, Matt found had lost interest in the other fish, instead devoting all of his attention to helping his prize pet thrive.
After bumping the creature with his tongs while rearranging plants in the tank, Matt also realized that touch triggered bioluminescent bursts from the creature. As he more deliberately rubbed its skin, the creature rewarded him with amazing lightshows. Matt had suffered from insomnia for almost his entire life, but he was surprised to discover that the creature's soothing lightshows quieted his racing mind and helped him sleep more soundly than he had since he was a child. As a result, his night-time routine had settled into a pattern of gently stroking the creature and letting his mind peacefully drift until he staggered to his bed and immediately fell into a dreamless slumber.
It was a routine that worked perfectly for Matt... until now. Tonight the routine had started like normal, but for some reason the creature had reacted more strongly than normal to Matt's touch. As his eyes were locked onto the increasingly bright and complex waves of light flowing across the creature, Matt could feel it swirling energetically around his hand.
He dimly realized that rather than responding to his touch, the creature was now coiling around his motionless hand and beginning to slowly flow up his wrist. As the creature pulled more and more of its long, slender body out of the tank and up his arm, faint alarm bells began to ring in his mind--initially out of concern for the cephalopod (which he assumed would be endangered by leaving the tank)--but then by a growing feeling in his gut that his prized creature was actually some kind of predator... and he was the prey.
The transition from zoned-out placidity to a full-blown fight-or-flight reaction was surprisingly sharp and sudden for Matt. But as he bolted into the empty alley behind his apartment building, he realized that a) he was completely naked, and b) he had no plan to deal with this situation. He slowed down and began concentrate on pulling off the long, twisting tentacle that now covered most of his slim torso, but was shocked as he felt hundreds of needle-like stings across his chest and back. Matt was startled and yelped in pain... at least he felt the impulse to yelp, but realized that the impulse had faded and withered somewhere well before it got to his diaphragm and vocal cords.
As he slowed to a stop, the tension in his body gradually drained and his hands slowly dropped to his sides. Matt was initially confused as to why his body was no longer panicked when his mind was racing, but as he felt an increasingly dominant presence in his thoughts, he realized it was because his body was no longer his: it now belonged to his Master. As his eyes began to glow with the same blue bioluminescence as his Master's, Matt calmly walked back to his apartment.
Still completely naked other than the adornment of his Master's tentacles, he fluidly sat down at his computer and calmly began to order thousands of dollars worth of fish tanks and cephalopods. Soon after that, his exhausted body was finally allowed to fall into slumber. But this time his sleep was not dreamless; instead, his Master filled his head with visions of how he would devote all of his time and resources to nurturing the growth of many more cephalopods... enough to ensure that his friends, coworkers, neighbors, and basically everyone he knew would soon get a Master of their own.
See https://www.deviantart.com/glaringeye/art/That-s-What-You-Get-for-Sleeping-in-the-Nude-GIF-1364443252 for an animated gif illustrating this story. The video was generated using Grok Imagine.