Mirio knew something strange was going to happen the moment Lily left for the sleepover. She was practically vibrating with excitement as she bounced out the door, hugging her oversized yellow jacket close and carrying a translucent tote bag full of snacks, slumber party games, and five different flavored water bottles.
"I'll miss you, hubbyyy~" she said, kissing his cheek with a wet smack.
"You're only going for one night," he said, wiping his face. "Try not to melt anyone."
"No promises!"
The sleepover was hosted at Vera's place—a friendly but slightly grumpy lamia girl with a big apartment and an even bigger heated floor space. Along with her, there was Clari the harpy, soft and feathered and always flapping when nervous, and Kuu, a sleepy-eyed snow oni who rarely spoke but loved warm tea and plushies. Lily had been thrilled to be invited. It was her first "official monster girl bonding night," as she called it, and she was determined to make a good impression.
Everything started fine.
They painted each other's nails (or surface equivalents), shared embarrassing crush stories, and played truth or dare—Lily gleefully dared Vera to wear a frilly nightgown two sizes too small, which nearly caused a tail-strangling incident. The floor was covered in pillows, blankets, and the occasional spilled bottle of soda. Giggles filled the room like the sound of rainfall made out of chaos and sugar.
By midnight, the lights were low, everyone had changed into sleepwear, and the four girls were curled up in a heap, breathing softly beneath a sea of quilts and fluff.
That's when Lily's core pulsed.
Just slightly.
The air in the room was humid—courtesy of Clari leaving the window cracked, and Vera's heated tail coils keeping the floor warm. Lily, dozing peacefully with her cheek squished into a pillow and one thigh lazily spread across Clari's leg, began to absorb moisture without realizing it.
Her body expanded.
Slowly at first—her hips swelled a little rounder, her chest lifted and grew, her thighs filled out like plush cushions under the blanket. The other girls murmured in their sleep, unaware.
Then her arm flopped outward and smothered Kuu's face.
The oni girl grunted.
"Whuf—cold jelly…?"
Clari blinked awake next. "Mmh—what's this pressure on my wings…?"
Then Vera stirred.
"Is someone… sitting on me?!"
By the time Lily blinked open her eyes, her body had doubled in size—her boobs now overflowing into two separate sleeping bags, her butt having flattened Vera's tail into the floor, and her thigh stretched across the entire group like a warm, jiggly barrier.
She looked around in confusion, still half-asleep.
"Mmnnnh… big dreams…?"
Vera yelled. "LILY!"
Lily sat up quickly—bad idea. Her chest surged forward, smacking Clari directly in the face and sending a pillow flying across the room. Her hips bounced with a full ripple that knocked Kuu's tea thermos off the table.
"Wha?! I—I'm big again!?"
Clari flapped frantically, her head stuck between Lily's boobs. "Mmph! I can't breathe in here!"
"Sorry! I'm sorry! I think I… I grew in my sleep!" Lily yelped, trying to back up—only to roll over Vera and smother her completely with her plush rear.
"Get your gelatinous butt off me!" Vera shouted, her voice muffled.
Lily gasped and sat up straighter—only to fall forward and pancake Kuu beneath her stomach.
"…Warm," Kuu muttered drowsily.
The room became a battlefield of soft chaos.
Blankets tangled. Feathers flew. Slime jiggled.
Lily's curves bounced with every frantic shift, her body now filling nearly half the room and expanding in every direction like a sentient beanbag.
"I—I didn't mean to! The air's too wet!" she cried.
"You wet yourself this big!?" Vera yelled.
"No, I absorbed it! Passively!"
"Stop absorbing things!"
"I can't—my thighs are full of moisture!"
Clari finally popped out from Lily's cleavage and took cover under a futon. "Why are your boobs so… tall?! They're like furniture!"
Lily whimpered and curled up slightly, her goo stretching as she tried to reduce her size—but it was too late. Her hips sloshed and filled the corner of the room, her butt resting squarely on three pillows and what was left of a plush bear.
"I ruined everything…" she muttered, deflating emotionally more than physically. "First sleepover… and I squished everyone…"
Vera, now upright and covered in bits of jelly and her own frazzled hair, paused. She looked around at the scattered girls, the broken tea thermos, the soft glow of Lily's gooey core in the dim light.
Then, reluctantly, she sighed. "…It was kind of warm, though."
Clari peeked out. "And squishy."
Kuu raised her hand from beneath Lily's thigh. "Still warm."
Lily blinked. "Y-you're not mad?"
"You body slammed me," Vera growled. "But I've had worse roommates."
Clari fluttered up and hugged Lily's shoulder. "It was like being caught in a warm marshmallow avalanche."
Lily teared up. "You're not going to un-invite me?!"
Kuu mumbled from the floor, "Sleepovers need at least one near-death experience."
Lily let out a gooey sob and hugged all three at once—accidentally knocking Clari over again with a full-boob nuzzle.
"I love monster sleepovers!" she wailed.
"Okay, okay, stop growing again—!"
Back at home the next morning, Mirio opened the door to a half-melted Lily dragging in a tote bag and a scarf wrapped around her wobbly waist.
"Sleepover good?" he asked.
"I might've expanded."
He raised an eyebrow.
"But everyone lived! Mostly!"
He patted her soft cheek and kissed her forehead. "I'm proud of you."
"Can I do another?"
"Not until we reinforce Vera's floor."
"Yayyy~"
And just like that, Lily's sleepover career was officially off to a squishy, oversized start.