When the girls of class 1-A of Creampie High first gathered in the classroom on the first day of high school, there was the usual tension of meeting a lot of new people you would spend the next three years with, and hopefully make some new friends for life. It was an all-girls school, with futanari allowed, so the sexual tension was high as well. Some were already getting to know each other, chatting while feeling up each other’s bodies, and some of the girls who already new each other were already fucking in front of their new classmates. There would be much more of that to follow anyway, so there was no need to be shy.

No one batted much of an eye at the various species of people gathered in the classroom, it was a long time ago that Humans considered themselves the masters of creation, but one of their new classmates still stood out like a green thumb - a slime. Of course, everyone had heard about slimes in history class, but actually seeing one in real life was very rare nowadays. Usually craving wet or damp places like lakes, riverbeds or dank caves to maintain their physique, they were ill suited to modern city life, and preferred to live in colonies in the wild. But here it was, in the form of a (somewhat) human girl.

When their homeroom teacher came in, everyone tried to cum quickly to restore some order, and sat down for the introduction. Everyone stood up, one by one, and presented themselves with name, interests, three measurements (plus length and girth for futanari) and sexual kinks. Everyone seemed like fun and interesting people, and the teacher hoped they would have a fun time at Creampie High, and promised to meet everyone personally and get a more hands-on session with them eventually.
And lastly, the slime. Since no one had seen one in reality before, they all stared at “her” (slimes are genderless, but this one was clearly in female form of its own choice) translucent body and slightly offset mimicry of a human. She didn’t seem slimy on the outside, but her insides were swirling slightly like the dust in your eyes when you close them, as she moved.
The teacher called her up to the front, and presented her as Blibba Blop, a slime introduced to the class by the headmaster personally, on Blibba’s apparent request. She couldn’t speak, other than making cute bloopy noises, but otherwise seemed to be on a human intelligence level.

The teacher finished his presentation of her with some final words as he pulled down his pants. His dick sprung out, and the whole class hummed appreciatively at its size, while Blibba took it in her hand and stroked it to hardness with a smile.
“Finally, there’s one thing slimes like more than anything else - human bodily fluids. They need moisture to stay alive, and what you may see as waste products are very nutritious to her. So make sure to cum and piss as much as you can in and on her, whenever you can.”
And with that, he sank his big cock right through her outer layer and inside her slimy core. The whole class cooed at the display, and Blibba blooped happily.
“While - unf- she’s not sticky on the outside –” the teacher panted while slamming his hips into her bubbly behind, making her whole hip area ripple like waves, “– her insides are hot and wet and grips you like a vacuum, so you futanari girls, make sure to have a lot of fun with her - you can stick your dicks in anywhere on her body!”
Blibba nodded eagerly and made a series of hand gestures, pointing at herself, making gripping gestures and a thumbs up.
“She can adjust her density and form to each one individually, and -haah- make sure everyone gets an optimal experience – fuck, this is too good, I’m gonna cum inside your body!”, the teacher grunted and did so, thick, long spurts of cum that everyone could see swirl around inside the slime’s body, until it was dissolved into her being. Blibba smiled as the teacher pulled out of her, his dick completely cleaned of every trace of cum, she had absorbed it all. She swept out her arms towards the class with a big grin on her silly jelly face, and then back to herself in a loving gesture and a cute “bloop-bloop”.

Everyone cheered, and the futanari girls scrambled to try her out. First in line was Emily Dickens, a small red-haired girl with a dick longer than anyone’s, already at high mast and slapping her in the face.
“I’ve dreamed of this…”, she muttered giddily to herself. “I can never fit my whole length into anyone… Please take me in.”
And Blibba did, positioning the almost meter-long penis around where her butthole would be, and let Emily slowly sink the whole length of her mighty member into the the slimy warmth, reaching almost up to the slime’s throat.
Emily looked like she could cum already, and it only took a few strokes, slowly pulling out and them slamming back in, before she did. The girl cried out as her white, swirling cum filled Blibba’s head and chest cavity to the slime’s apparent delight, before it slowly dissolved. Emily wasn’t satisfied yet however, being inside the feeling of a pussy with her whole length for the first time, and kept slamming into Blibba’s butt as she grew hard again. More girls wanted to join in, though, and Meridia, the giant amazon, put her massive dick into Blibba from the front, getting a boob job - inside her boobs. Blibba grabbed the closest dicks on each side of her and started to give them handjobs, slowly easing their dicks inside her hands and arms as they too were given the slime onahole treatment until they all came inside her body, to everyone’s delight.

From that day, even the bigger futanari girls would always have someone to empty their cum into when their classmates wouldn’t suffice, and Emily made sure to get the seat beside Blibba, and started to fuck her every break.

Bonus (P):
Since Emily’s dick was so long, even flaccid, she could easily point it over Blibba’s body and just let loose any time she needed to pee with her dick bladder. Blibba just absorbed it all without any spilling, even when Emily pissed in her lap for a full minute. Emily still emptied her vagina bladder where she sat on the chair, forming a hot lake around her legs, if it was in the middle of class, though. That’s the usual way, and all girls are doing it.