A little persuasion...

The creature began warbling in a tongue unfamiliar to Myria, sensing her confusion it swapped to another language, and then another, studying her features carefully.
... "Ever so dull when I have to go through this rigmarole- " It said, and Myria's face lit up in comprehension. The creature smiled.
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"It's been a while since one of your kind visited" It mused. "No matter, I'm sure this will prove most beneficial in any case. I have fond memories of your kind."
Myria's eyes narrowed. "Fond memories? It's really going to be that bad huh? I thought the toads were bad enough."
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"Why my dear, rest assured, I mean you no harm. On the contrary, I intend to help you. Though... This help would come at a price..."
Myria rolled her eyes, "Let me guess, virgin sacrifice? Eternal ****? The firstborn of of each family living near the cave?".
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"Heavens, no. My your kind have developed some strange habits in the times past..." It tutted, "I only seek a companion. One to keep me company, in this darkness. A... Mate if you will".
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"Sounds suspicious, how do I know you don't just eat your mates. Or use them like the frogs do?" Myria ventured.
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"Such accusations... I exist only to prolong the life of my partners, keep them happy and should they wish, procreate. I was placed here as a "last ditch measure" should catastrophe strike the world above. The fluid you ingested, added several years to your life span already, and is setting to healing your long-standing ailments. The scar on your arm for example, has been completely healed. Better than new even."
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Myria's eyes grew wide as she realized it spoke the truth. She was feeling fitter than before she'd entered the cave. The scar had vanished. The promise of youthful and long-lasting life... It was sounding tempting.
"What about that procreation thing? Is that lethal, a one time deal or something. There has to be a catch, surely." Myria said, trying to alleviate the thoughts forming in her head.
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"I assure you, perfectly normal for your... Physical standards. Though I'd venture, it would be a great deal more pleasurable than a regular male of your kind... Would you like to experience it? You do seem quite ready." It mused as its vines and hands resumed their stroking of her delicate areas.
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"Vermael.. I-" Myria started, just as a vine brushed against her swollen clit. She struggled to keep her eyes focused as two more vines encircled her breasts, coiling round them while teasing her erect nipples. She tried to fight off the urges, but each slithering vine, that caressed her quivering form elicited shivers of pleasure. Her breathing came raggedly, as her body betrayed her more with each passing second. She squirmed, mid-air in equal parts pleasure and revulsion. Finally she snapped.
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"Fuck me then! Show me how much pleasure you can give me!" She cried out.
The creature with a knowing smile, obliged and twitched its head, after which the vines lanced forward to bring the real pleasure. A vine pushed deep into Myrias pussy, finding her cervix upon the first stroke. Even so, it pushed deeper, coiling and wrapping itself inside Myria's pussy, stretching her walls and stroking so many places that had not yet been touched within her. The vine then retracted slightly, so what remained outside could start pistoning her pussy, while what was inside her wriggled and twisted relentlessly, emitting obscene sucking sounds. Myria overcome by this rush of new sensations moaned and screamed within equal measure.
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As she did so, the vines surrounding her breasts grew tighter, bouncing them in a different rythm to the rest of her body. Multiple vines slithered over and around her nipples, creating suction, rubbing and slimy sensations all at once. The vines then pressed her breasts together, as a third vine slithered over her stomach and between her mounds. It coiled loosely around her neck, hitting both sweet spots beneath her ears, as the end of the vine prodded in her mouth again. This one also leaked the sweet nourishing liquid, which Myria now greedily gulped down, even as the vine rhythmically attempted to push deep down her throat.
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Myria, by now going delirious, with the obscene amounts of pleasure rolled from one orgasm, to another, twitching uncontrollably in the embrace of the vines as her hips made obscene thrusting motions towards her lover. The vine suddenly, wholly withdrew from Myria's pussy with a huge slurp, eliciting a moan between disappointment and pleasure from her. She was still basking in wave after wave of mini-orgasm, yet the loss of sensation deflated her. She suckled enthusiastically on the vine in her mouth, to try to get the creature to resume.
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Then she felt the slick tentacle prodding at her ass, as another thicker vine began caressing her mound, causing her pussy to almost froth in anticipation of what was to come.
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Then all motion stopped, as the creature looked Myria in the eyes. The dark eyes twinkled knowingly, and a smile formed on its lips.