Taking a fleshy stab at it.

It's no secret to anyone who asks that I have a thing for tentacles. I watch the hentai, peruse the manga, collect plush Cephalopods and have a Lovecraft fetish.
So I thought, why not try to write it myself? But rather than rape (and not to sound like a zoophile here, as I have no delusions about interspecies consent) what about tentacle lovin'?
So excuse the following vulgar short story.

...

With the soft, mindfulness of a lover, she eased the creaking door to the green house open. Inside, it was like wading through water, the air thick with moisture that dampened her skin, hair, and glistened in tiny sparkles caught on the fine fraying of her uniform. Filled to the brim with tropical and exotic plants, inside the cramped green-night glass house, crawlers, fungi, flowers, vines, palms, bushes and lush mosses created a heady, dizzying scent. But it was nothing compared to her pride and joy, the main event. In the centre of the green house sat a squat green (that was once white) bath tub, nearly overflowing with aquatic plants, weeds and algae. It wasn't even the plants. Beneath the surface was the reason she had cultivated this cornucopia of lurid, damp vegetation. To make him feel at home.
Quietly, ever so quietly, she pulled up a slimy chair and sat in front of the tub, careful not to startle him. Instead, she slipped off her shoes and panties, both dampened by the humidity. Placing her feet on the edge of the bath tub, she slowly sucked her fingers and ran them along her moist pink slit, and again, and again. She repeated and let her own heady scent amongst the flowers waft over his water. Her small bead of pleasure was swelling, and things moved beneath the surface. Juices pooled on the seat, and she reached into her school satchel and pulled from a paper bag a red raw, juicy sliver of meat. Diluted blood and icewater ran down her forearm as she took the flesh and dragged it slowly up and down her wet cunt. She let it sit in place, and, leaning forward, lazily dipped her blood and juices drenched fingers, and her lover, very awake, brushed her from beneath the water's surface, licking her clean with a long tongue. A single eye on a stalk rose from beneath algae blooms like a submarine periscope, and a small, lonely black pupil under a murky green membrane swivelled to look at her, her parted, waiting mouth, pert nipples captive in a tight button-up shirt, and her swollen, dripping pussy, adorned with raw meat.
A tentative tendril rose and half slithered, slowly, cautiously, towards her, and with a delicacy and care, extracted the sliver of meat and returned to the water, and there were slight ripples as he gorged himself, and she moaned with anticipation.
"Come..." she crooned, again doubling over and leaning over the tub's pond surface. A thick, turgid tentacle rose and traced her lips slowly, and she kissed it tenderly, and it slipped between her lips, and she sucked hungrily. She arched her back, and beneath his water he moved with her, and a second and third tentacle wrapped themselves around her small ankles, and a fourth landed with a sucker squelch on her pubis, and slithered up her stomach and between her generous breasts, and pulled back towards itself, ripping her shirt open and she grinded into the air, moaning into the tentacle in her mouth. Arms circled her tits, coiled and squeezed her erect nipples, and she was dripping wet, and her eyes looked imploringly at his single stalked eye still floating in the water. Fuck me. she begged.
With a heave and an unpredictable speed he pulled himself from the water, a giant squid-like creature, with many suckering, hungry tentacles. His huge, bulbous mantle was pulled back from his body like a foreskin on an erect, throbbing cock. He placed his centre around her cunt and the thickest, slimy phallus with a mind of its own, with a head like a squid mantle, teased her red pearl. Tears ran down her cheeks, and with a gasp, he thrust himself into her, hard and fast, fucking her pussy relentlessly, roughly , holding her in place as she moaned, wriggling against him, but he held her arms and legs fast. She ran her mouth up and down his tentacle and moved her hips with him gasping and groaning with his massive erect form inside her. Suddenly, he turned her around, his tentacles guiding her until she was bent over the chair, and finally, fucking her hard, a last small tentacle slipped wetly in and out of her anus. Her moans of ecstasy were stifled by his tumescent tentacle, and she felt a low, golden pleasure rippling up her lower stomach, and tingling in her whole being. Her juice was running down her legs as he pounded into her, faster and faster, and she knew they were both about to come. Her legs tightened, and all her muscles contracted, and white hot sensation explode in her crevice, and she felt her whole cunt clench and squeeze him just as he ejaculated, warm and creamy, so profusely it exited everywhere. They both shook in absolute bliss for moments as he thrust into her a few last times, his seed shooting up in her and trickling down her legs and stomach. He shrank away from her, and receded into his tub with a splash, and she, gripping the chair with white knuckles, looked back at him with wide eyes, an engorged mouth and a throbbing that ebbed away, giving way to deep contentment. She bent over to pick up her discarded, soaking panties, but with a slimy tentacle still slick with her saliva, he grabbed her hand. Stay.
So she took off her socks and slid into the slimy, algae bloom covered bath tub with her lover and sighed deeply as he played with her hair, and she rolled over and felt post coital exhaustion creep up on her like a sneaky sunset, and she fell fast asleep.

THEY LOVED EACH OTHER VERY MUCH AND LIVED HAPPILY EVER AFTER.
THE END