Mary told Sencia to clean up the kitchen of the dirt and pottery shards scattered around, and then to do a quick cleaning of the rest of their studio apartment. The nude servant was all to eager to obey, rushing to hands and knees to clean. As it did Mary smiled and returned to her box of wonders. She lifted the box of Magic Vials from its resting place and moved from the kitchen to the living room. She set it down and took a deep breath. Rather than immediately rush into working on the vials she picked up a pad of sticky notes and began to take notes.
"Symbiote." said the first, with the words "Internal/External Parasite" added beneath. Mary set this to the side and added several other items. "Fertility", "Egg-laying" and "Spawning" were set out as other options. Then after a pause she wrote out "Fictional Beings?" and set this in front of the Vials itself. She paused and pictured in her mind a symbiotic alien from a comic book she had read recently. Opening the drawer she saw the vial, pure black goo with a symbol of a neuron on the cork. Her heart skipped a beat. She closed the drawer and thought about dragons and about orcs. Opening the drawer revealed two new vials, one green and one shimmering gold - glowing with an internal warmth.
Victoriously, Mary put a check mark beside the Fictional Beings note and stood, quivering with excitement. She moved towards a nearby bookshelf and started to take down books. Mary's library was small, and more than half made up with books from one of her main hobbies - playing Ogres & Oubliettes and other roleplaying games. The stack of books included a half dozen creature collections and bestiaries that would provide her with ample fodder to satisfy her desires. With these in hand, she wondered if the issue would be finding the traits - or simply picking out how to go about what she wanted.
She found herself wondering, what did she want, exactly. She knew that she had this deep deviant fascination with sexual parasites and symbiotes. Things squirming into people and living within them, empowering them even as they corrupted and pleasured them. She wanted that for herself, wanted to make Sencia into this sexual symbiotic thing. So she set to work with the vials and with her books.
It took half an hour, maybe more and Mary found herself getting flushed and excited by the prospective of these changes. She had nine vials to work with, so she set to it. First the reality and resist reality vials. She wanted Sencia to know they had once been human, even if the rest of the world accepted it as normal. To this she added the alien symbiote vial, thinking "Permanent Symbiotic Connection Granting Powers". Then a vial from an oversized leech, thinking "Body". A vial from the squidlike psyche flensers, thinking "Psionic Powers". Squirming, pressing her legs together, she pulled out a vial for pinworms, thinking, "Uterine Endosymbiote", imagining the new leechlike Sencia crawling inside her, taking up a home in her womb. She could feel herself getting wetter and wetter. A vial from a serpent, focused on laying eggs was followed by a vial associated with an elf, "Immortality". Shuddering she nodded and looked at the last remaining slot in the mixing tray. She thought she had what she wanted, but it was still so very tempting to add a little more. So with the last one she simply slotted in a poison dart frog vial, "Bright Coloration".
She pressed the mixing drawer closed and squirmed, glancing over to where Sencia was fastidiously scrubbing the windows of the apartment. It took only a few brief second for the drawer to pop open with a chunking noise once more and Mary shivered with anticipation. Standing, vial in hand she moved to Sencia's side.
"Sencia, sweetling." Mary said, her heart racing, "Drink this for me?" The vial was a swirling black and purple miasma that seemed to pulse and throb in her hand.
Sencia did not even ask what it was, so deeply was her mind devoted to serving Mary. She simply took the vial and tipped it back, gulping down the thick goopy liquid. The change was slower than her growth to a human and the whole time Sencia - whose mind was unchanged - screamed in terror. Mary trembled and simply watched, feeling the trembling heat between her thighs, the wetness down her legs as Sencia shrank down, skin going from tan to bright blue. Its features grew softer, covered over with a layer of flesh that quieted its screams to muffles. Sencia trembled and writhed as her arms and legs fused together, brilliant yellow spotting appearing on her body even as it started to grow slick with slime. She flailed, head and neck pressing down into her torso and her genitals smoothing down to nothing. She slowly flopped to the ground, boneless, as new orifices opened at the tip of her shrinking body. One at each end, though Mary could not tell you which was which.
It was then that Mary started to hear Sencia's panicked cries in her mind, hear the fear in the trembling symbiote, hear the love it still undeniably and perhaps inexplicably had for Mary. As its growth stopped, leaving it a brilliant neon colored leech thing the side of Mary's palm. Mary shivered and spoke out loud. Sencia was telepathically begging for an answer. "We're going to be together forever now Sencia. It's...it's my gift to you. I know it seems scary but you have to trust me." She began to unbutton her jeans.
Mary was chubby, and getting the jeans down over her thick thighs took a moment, her unshaven pussy revealed to be dripping and ready. She left her top on over her round belly and average breasts. She had never loved her body but in this moment she was excited by it, by what it could become. She bent down and gently, reverently lifted the quivering leech form of Sencia and whispered to it, "Crawl into me, my sweet." She leaned back, heavy ass supported by the back of her couch, and gently pressed one end of the Sencia-symbiote against her aroused sex.
The sensation of its slimy skin touching her made her heart skip a beat. It was like a jolt of intense electrical pleasure. And as the Sencia thing squirmed and started to slowly enter her Mary had to drop her hands to hold onto the couch, gasping and groaning. The leechlike thing was squirming slowly in under its own power - half hanging out of her lewd and dripping pussy. Mary groaned, feeling Sencia's mind touching hers even closer, feeling them distinctly sharing the same mental landscape but still separate. Sencia, despite its fear, seemed excited now, eager to please and seeming to feed off of Mary's energy.
Mary's hand lifted from the couch now that she had steadied a bit and slid her hand down to her clit, gently circling the pearl of flesh and panting, quivering, as Sencia slid in. Even before Sencia was fully in Mary had her first orgasm in months, shuddering and spasming. This only fed Sencia more and the thing squirmed more vigorously, sliding in further. The next orgasm came quickly, again and again and again. An hour later, drenched in sweat and emerging from a haze of bliss that almost made Mary forget who and what she was, she felt the Symbiote settling inside her at last, quizzical, equally spent, but with a touch of fear still.
Mary could feel something though, could feel her shaking tired flesh changing. She could feel Sencia squirming inside her. Sencia's panicked telepathic sensations letting Mary know that even if the Symbiote wanted to it couldn't stop. It was binding with her, consuming and replacing organs and flesh to make a more perfect host. Mary realized with a stunned shiver she wasn't sure just what that host would be. Had she gone to far? Would her own fantasies be her undoing?
She squirmed and, with few other options...