Harley stared at the vial of thick black slime, slowly waiting for Joker to return from his fight with Batman. It was a weird thing, straight out of a parallel universe Joker had said. They claimed it was an alien, a parasite, able to latch onto any human and give him or her strength beyond imagination. If that's true, then maybe…

"Maybe if I was stronger, Mr. J wouldn't have me cooped up in here watching over this stupid thing..." Harley lamented, sighing deeply. "Maybe... I would be out there, fighting him him... side by side..."

She swirled the slime around the vial as the goo began to twitch about, as if reacting to her desires. She wanted power, and it wanted her. Maybe it wasn't a parasite, maybe... a symbiote…

Harley stood up, violently flinging the vial to the floor as it shattered, freeing the slime from its glass prison. The goo began to expand rapidly, increasing in mass as it pooled below her.

"Ya want me don't ya, lil' alien? Well here's your chance to take cute lil' Harley!" Harley announced, arms akimbo and preparing for the worst. The slime began to sprout tendrils which wrapped around her legs, oozing over her feet as it dissolved her skin-tight costume little by little. It latched onto her delicate skin bit by bit, coating her legs entirely within itself as it crawled up her thighs, sensually massaging her inner thighs in the process. "Ooooh myyyy..." Harley sighed, feeling the light stimulation by the alien, unable to deny its pleasure.

Harley was definitely getting aroused now, evident by the growing patch of moisture at the fabric of her crotch. It felt wrong... this was an alien, a slimy goopy alien, and yet it was actually making her horny. "Now now Slimy, it's not nice to make a girl ooooooOOOOH!~" Harley yelped as she felt gooey tendrils crawling and oozing between her buttcheeks, wrapping itself around her well-defined ass, putting itself within her. She grabbed her ass-cheeks by instinct, arching her back as the sensations of the slime invading her ass overwhelmed her. "Oh my... ooooohhh mmmmmmnnnn~" Harley moaned as she felt the slime stretching her anus slightly with its movements, latching onto her inner walls as it filled up her ever so deeply with its warm, slimy substance, forming a slimy butt-plug within her that simultaneously fucked her in the ass.

"Oh my god~!" Harley squealed in surprised pleasure, falling to her knees as the slime toyed with her asshole. More and more slime just kept crawling into her anus, oozing deeper and deeper into her ass filling her up more and more continuing to provide her with anal stimulation. She had never felt so invaded, and yet she just wanted more of the alien inside her…

"Ngh..." A moan escaped her black lips as slimy tendrils tore off her crotch piece, exposing her tight pussy to it. Slimy tendrils reached into her soft, delicate folds, spreading them open gently to reveal her moist virgin insides, pink and untainted. Joker never had the sexual interest, hence her innocence remained. Harley was throbbing... badly. Her pussy had never felt so desperate before, so... empty. She needed to be filled... completely, utterly...

"You want to go in, don't ya..." Harley cooed seductively to the symbiote, wriggling her hips and offering them to it. "Well come on, don't make a lady wait~"

Responding to the blatant invitation, the slimy tendrils plunged into her nether lips, invading her with its dark substance. "Aaaaaahhhhnnn~" Harley moaned out, falling on all fours as she felt gooey tendrils latching themselves onto her delicate inner flesh, coating her insides completely with itself. More and more slime penetrated her deeper and deeper, eventually pushing itself through her hymen, taking her virginity. As tendrils latched themselves onto her engorged G-spot, Harley let out a pleasure-filled gasp as the slime began to engulf the erogenous zone, prodding and rubbing against it much to Harley's delight. The pleasure built quickly as Harley gripped onto the puddle of slime below her for support, wriggling her hips in pleasurable discomfort.

"T-that's it, I'm gonna... gonna..."

"Cuuuummm~!" Harley moaned out, feeling herself release as her inner walls flexed and clenched her gooey intruder, cumming straight into the alien as pleasure flooded her mind. The pleasure knocked her back onto her butt as Harley spread her thighs apart out of pure lust, inviting more tendrils to crawl into her throbbing, cumming slime inside her pulsed rhythmically with her own orgasmic convulsions, intensifying her climax and prolonging it to what felt like forever. Just as the pleasure died down, Harley suddenly spasmed as she felt herself cumming again, her convulsions pushing its goodness deeper into her vagina.

"Aaaaahhhh... aaaaaahhhh!~" Harley moaned as more and more slime entered her pussy, pushing against her inner walls giving her the sensation of being "filled". Once Harley's vagina was sufficiently filled with the alien, acting like a gooey, all-encompassing living dildo, the tendrils began to latch onto her soft folds, coating her pussy delicately as tendrils wrapped around the entire length of her erect clit, sending sparks of pleasure through her throbbing pussy and causing her to cum again.

"Oh god~! It's… it's totally inside meeee~" Harley moaned, wriggling her hips feeling the alien goo inside her. She had never knew how… empty… her pussy was… until someone- or something… filled her completely.

With her holes completely plugged up and her clit completely engulfed, the slime proceeded to coat the rest of her body, its tendrils wrapping around her waist as others began to coat her belly. When it reached her ample chest, the slime's tendrils began latching onto her soft, tender breasts, inciting a pleasure-filled moan as her breasts were delicately covered with an even coating of the alien. As it did, the slime gently squeezed and massaged her breasts with itself, bringing Harley to an indirect orgasm.

"Oh godddd~" Harley squealed with childish glee, feeling the alien pushing themselves into her nipples, causing Harley to cry out in unexpected pleasure as her breasts were filled with the gooey slime, stimulating them from inside out as they grew to a firm size D. As the last tendril disappeared into her breasts, the slime then wrapped themselves around her erect nipples, completely encasing her breasts in the shiny, black alien.

Harley could not think straight anymore. All she could feel was pleasure from the alien as it coated the last of her lower body. She could feel it against every inch of her skin, coated against her body in a slimy, stimulating bodysuit, squirming and rubbing against every sensitive area of her tender body... the alien slime forced her into another orgasm, saturating her pussy with invasive pleasure. As Harley opened her mouth to moan, she was greeted with a flurry of tendrils, crawling straight into her mouth as it proceeded to coat everything. The slime coated her tongue in a delicious embrace as the rest oozed down her throat. Harley swallowed obediently as she felt the black nectar sliding down her gullet, going deeper into her body. More and more slime began to rise up as tendrils latched themselves onto her face, preparing for the final bond. Just then, the slime began crawling into her ears as Harley squirmed in uncomfortable pleasure, feeling the slime oozing deep into her head. The slime then latched onto her brain, sending its branches into it as it corrupted her already unstable mind even further.

Harley Quinn... let us become one... A voice rang in her head.

"Yes... yes... become one... Mmmm~" Harley swooned as she came in unison, lost in pleasure.A mass of black slime hovered over her face, ready to complete the transformation. Without hesitation, Harley accepted.

"Yes... take me~!"

The mass of slime fell onto her face, latching onto her skin like a living mask as the slime sent her erogenous zones into overdrive. The twisted face of Venom emerged as Harley came like she had never came before, climaxing into her new suit, her new "other"...

"AAAAAAAAAAAAAAAAHHHHHH!~"

Dizzy from the intense pleasure, her symbiote then began peeling off her skin as tendrils crawled down her body, diving into her ass and her pussy lips. The slime crawled deeper and deeper into her, placing themselves in her holes. Oozing through her cervix and into her womb, it rested snugly inside her uterus. As the last of the slime disappeared into her pussy, Harley blacked out.

Harley woke up, completely naked and drenched in sweat. Her pussy was warm and throbbing as she sat in a puddle of her thick, translucent pussy juices. Standing up and looking into a nearby mirror, she saw her skin had turned completely white from head to toe, just like Joker, complete with pitch black lips and her hair tied into twintails. It wasn't simply makeup either; her skin colour had completely been altered to suit her desires.

Do you love it, my host...? A childish voice echoed through her head.

Harley jumped. "W-what exactly are you?"

The voice giggled. Oh Harley… I'm the alien you just put on… can you remember~?

"Aaaaaahhhhnnnn~" Harley moaned suddenly, knees buckling as she suddenly came for no reason. That's when she felt it… that firm, gooey mass of slime inside her pussy sucking on her inner flesh, absorbing her love juices as she generated them, leaving her clean despite her lewd sensations.

As the pleasure died down, Harley finally got a better look at her new body. She was curvier, bustier, fitter… her skin no longer had a single flaw, being totally smooth and supple like silk itself. She… was actually in love with herself now.

"Mmm yes..." Harley said, running her hands over her new body, feeling the symbiote inside her, her holes filled up her its gooey substance. Her hands roamed upward, playing with her new, supple breasts that defied gravity. Inside her boobs, she knew, the alien was snugly fitted, almost like a living implant. As if rewarding her for her acceptance, her symbiote then rubbed itself against her G-spot, bringing Harley to a slow, lovely orgasm as pleasure surged through her pussy, her juices dribbling out as her symbiote couldn't keep up with her "production".

"Ah!~" Harley yelped as tendrils suddenly began crawling out of her holes, latching onto her skin as they emerged. The simultaneous emptying of her womb and her ass made her cum hard as tendrils wrapped around her erect clit, intensifying her pleasure. Before long, the slime had completely coated her entire body within itself, stopping short at the edges of her face allowing her to revel in the pleasure of being completely coated by its substance. Harley's blushing pale white face contrasted against the slime's striking black tendrils as she moaned out in satisfaction, feeling the symbiote plugging up her holes with itself as it squirmed about all over her body, keeping her in a constant state of arousal.

"Yesss~" Harley moaned as she came, the symbiote tightening itself around her body in response. She hugged herself in her blissful state, savouring her bond with the alien as pleasure flowed through her body, wrapping her in warm ecstasy. Just then, the door burst open, sending in a stream of bright street lights flooding into the dark room.

"Oh Harley? I'm back with the groceries!"

Joker strided into the halls, cockily dragging an unconscious Batgirl behind him. As he turned to Harley, he stopped at his tracks, a mix of rage and wonder in his eyes.

"Harley. What. Did you do...?"

Harley quickly skipped over to Joker cheerfully, twirling around to show off her "achievement". "See Mr. J? I bonded with that alien I was protecting~! It was kinda weird too..." Harley explained. "It went everywhere, even some... private areas~" she blushed as she admitted it, the symbiote causing her to cum slightly as well. Joker pinched the bridge of his nose as he hung his head.

"Oh Harley... oh Harley Harley Harley..." He lamented. "Didn't I tell you we NEEDED THAT LITTLE BLACK THING FOR OUR PLANS?!"

Harley was taken aback at the outburst. "S-sorry Mr. J-"

"Don't Mr. J me now, you better damned well put that thing back where it belongs! … Or else..." Joker turned away, examining the heroine he kidnapped.

He... must…

"... what is it...?" Harley questioned the voice in her head.

Do not leave us host... he must... die…

"What? No! Mr. J's my... my..."

Listen to ussss…

"Ngh!" Harley fell to her knees as pressure filled her head. At the same time, the slime in her holes began to squirm, rubbing and grinding against her inner walls as it brought her to climax, making her cum over and over again. As she did, the symbiote spread its branches deeper into her brain, linking her desires with its own.

That Joker isn't important to you... to us…

"Aaaaahhh... Ahhhhhmmmm~!" Harley couldn't respond as pleasure flooded her mind, making it ripe for corruption.

We are made for one another... we are one…

"Aaaahhh... we are one..."

Joker means nothing... I love you... We love us…

"Aaaaahhhh... ha ha... HA HAHAHA~!" Harley giggled madly as her mind was recorrupted, her obsession with the Joker now converted to her acceptance to the alien symbiote. With one last orgasm, Harley stood up as the tendrils on her face inched further in, representing her deeper bond with the symbiote.

"Puddin'... Joker... Time to die~!"

"What-! AAAAAARGH!"

With a single thrust, Harley's arm stretched and pierced Joker straight through the chest. Blood splurted out of Joker's shocked face as he realised what Harley had done.

"Ha- Harley..." Joker spluttered as the light slowly faded from his eyes. The pure thrill of the kill made Harley cum once again into her suit as she retracted her tentacle-arm, licking the blood clean off her fingers in satisfaction.

"There is no more Harley now... hehehehehe~" Harley giggled in ecstasy. "Now... we are... INSANITY!~"