A young lopunny was wandering through the woods one day minding her own business, being quite an attractive young thing, her hips and butt were nice and wide and her boobs were the size of basket balls, her curves were just drop dead sexy, she being 7 feet tall, quite large for her kind and having Snow White fur with light blue highlights, she having a modest body and some what attractive curves. 
She wanders for a big till she came across a cave, wondering inside to see if anything was in there. The deeper she went the darker it got, but then she started seeing a faint blue glow. She got closer to the light to find it was coming from a strange glowing blue moss. She poked it gently and it glowed very brightly, she took a step back and slipped into a hole, sliding on the slippery blue gunk she fell deep into the earth till she came out onto the floor of a huge cavern where the walls were covered in the same glowing blue moss.
"Where the hell am I?" She asked herself as she got up. Her footing wasn’t very stable as the ground was very squishy, and looked like a huge pool of goop. She looked around for a way out but as she did she started feeling funny. Her loins started to feel warm, she ignored it for the moment but as time went by she started feeling very hot and her loins were dripping wet with need. "Wh-what’s happening? I-I can’t be going into heat already." She told herself, her paw already reaching for her wet muff and she started pawing herself.
She drops to her knees as her paw went deep into her sex, reaching for her g spot in her heated need, her mind struggling to keep its grip on her common sense as her sensitive ears picked up a soft gurgle behind her as the floor moved slightly, thick purple tentacles reached up out of the goo floor and moved towards her. Grabbing her legs gently and covering them in the deep blue slime they were made of and teased at her tight tail hole and another probed at her sex, two more grabbed her arms gently and pulled her paw away from her sex to be replaced by the thick goo tentacle.
She moaned loudly in lust as her cunt was invaded by the slimy tentacle, her tail hole was next making her moan even louder. With all this pleasure her mouth hung open and her tongue hanged out, allowing another thinner tentacle to push into her mouth. At first she struggled but whatever was in the slime started to make her very relaxed as it pumped a purple fluid down her throat and into her stomach, clear pumping sounds could be heard coming from the goo floor but it was more organic sounding, her throat bulged out with every large shot it pumped inside her, it stopped when a whole gallon was in her belly.
The slime she was force fed starts to affect her judgment as she started giggling like a stoner and she just fallowed the tentacle in front of her. the one in her sex started to pull out of her and then slammed back in, at the same time the one in her ass pulled out, they alternate this way slowly making her moan like a butch in heat. Her basketball sized tits bouncing around as she gets fucked. Her insides growing so hot and wet from all the slime being pimped inside her, it leaking out around the tentacles in her helping to keep them lubed up.
As she gets fucked more tentacles came out of the goo floor and started covering her in the purple slime, making sure to cover every inch of her fur as she hungrily took the one in front of her and sucked on it, wanting more of its sweet juice. Then two more came out of the goo and squeezed into her tight pussy, stretching it out farther than any normal woman could take. Harder and faster they fucked the poor lopunny and her mind slowly broke down all reason.
She took it like a true bitch as 2 more plundered her sex, they pounding away at her cervix and wearing down its resistance. Then they got through and invaded her most sacred life giving organ, filling her womb with slime, it leaking out of her around the invading members as two more coiled around her tits and massaged them, another two playing with her nipples.
She murred around the tentacle in her mouth as the two at her nipples molded around the sensitive teats and thinner ones probed them for the opening, once finding it they wormed their way down her milk ducts and into her boobs, stretching her nipples out in the process. Making her moan louder than ever as she came hard, then she saw bulges the size of grapefruits, they stretching her tight cunt open to her limit, eggs also started getting forced into her tits, stretching her nipples to their limit as well, slowly her belly and tits start swelling.
One by one the eggs get forced into her body, making the young Pokémon yell in bliss, she rubbing her belly and her boobs as they grew, showing lumps as the eggs get pushed into her body. She having a mind shattering orgasm from each egg that enters her body, soon her belly and her tits reached the ground and started pushing her up slowly. The eggs slowly get pushed into every part of her body, turning her into one big egg sack for the creature to abuse. She pants heavily as her body is stuffed full of the monsters young, this going on for a few days.
Her boobs and belly kept growing and her hips and ass swelled as the slime she was fed went to them adding to the size and softness, her mind broken and all she wanted was to be bigger and to be a good slut for her master, her belly and tits growing to 30 feet each and kept going, her cunt and nipples so stretched out they could take a full grown man into them. As she kept growing bigger and bigger she grew tighter and tighter, her belly and tits creaking as the eggs get pushed into them, they being at 60 feet each and nearing their limit.
By the time it finished with her it stopped filling her and her belly and tits were each 70 feet wide, creaking loudly like overly tight latex and as they rubbed against each other sounded like over filled balloons. She filled to her absolute max as the tentacles pulled out of her nipples and her cunt, but left the one in her ass to pleasure her as the one in her mouth fed her. She yawned around her feeding tube and fell asleep on her belly, rubbing it lovingly before closing her eyes. Enjoying being this creatures pet and incubator for its children. 

Part two will come based on your feedback and how much this story gets faved. it’s up to you to help me decide to post the second part.