Chapter Text
A violent pounding on Undyne’s lab door startled the scientist from her Mew Mew Kissy Cutie marathon. There was only one monster Undyne knew that knocked as if they were trying to break down the door. She paused her anime and rushed to the lab entrance.
Right before she hit the button that would open the door, she took a deep breath and smoothed out her rumpled lab coat. Now thoroughly prepared, Undyne hit the button. The lab door slid open with a hiss.
“A- Alphys! It’s so g-good to see you!” Undyne shyly smiled at the burly lizard monster that stood outside her lab. However, the serious expression on the captain’s scarred face made Undyne falter. “W-what’s wrong?”
Alphys opened her mouth, but closed it without saying anything. She looked down at her clawed fist and then thrust her hand toward Undyne. The timid scientist took an involuntary step back.
“MWEHEHEH! Greetings, Doctor Undyne! Surely you recognize me, the Sensational Sans!” A familiar voice squeaked. In Alphys’ hand sat an impossibly tiny skeleton.
“We have a small problem.” Alphys growled.
~
Sans stood on the lab counter. He wore only his blue bandana tied around him like a toga. He was smaller than most of Undyne’s colorful beakers. That meant he couldn’t be more than five inches tall.
The small skeleton let Undyne inspect him. She recorded his height and weight and took some other measurements. He was glad that Alphys had already returned to her royal guard duties so that she didn’t see him in such a helpless state.
He suffered through Dr. Undyne’s further poking and prodding as she excitedly rambled about scientific stuff that Sans didn’t really understand. Papyrus probably would’ve been able to explain it to him, his brother was smart like that. When she was finally finished, the tiny skeleton was tired and hungry.
“So you can return me to my naturally glorious stature?” Sans asked optimistically.
Undyne shook her head and blushed. “S-sorry, Sans. I can’t counteract the effects of the Shrinking Sauce.”
“You mean I’m going to be this size forever! How will I ever become a member of the royal guard?” Sans wailed. Bright blue tears gathered at the corners of his eye sockets.
“N-No!” Undyne flapped her arms. She hadn’t meant to upset him. The sight of tears made her panic. “The effects should wear off naturally in a few days!”
“Oh, I see.” Sans sat down and curled his short arms around his knees. He rubbed his face against them, feeling quite embarrassed.
A light touch on his skull made him peak up. Undyne looked concerned as she gently pet Sans’ skull with a blue scaly finger. Sans sniffled; this was all his fault.
“It’s okay. You didn’t hurt anyone. N-next time you know to read the directions more thoroughly.” Undyne consoled him.
Sans knew she was right. Undyne was a super smart scientist after all. But he still felt silly for drinking an entire bottle of Shrinking Sauce, rather than dabbing just a bit behind his ears. If only he had read the directions!
All of the excitement had drained his magic too. He hadn’t eaten since breakfast and now it was late afternoon. Eating would definitely help Sans feel better about everything.
“If you had any food to spare, it would be very much appreciated Dr. Undyne.” Sans politely asked.
Undyne slapped her forehead, just barely missing her glasses.
“Geez, I’m such a terrible host! Let’s get you some food.” She scooped up her friend and took him to the kitchen. The dizzy little skeleton was set down on the counter while Undyne began looking through her cupboards.
“I guess it would be difficult for you to eat ramen.” Undyne mumbled as she stared at shelves full of cheaply packaged instant noodles.
“Do you have tacos?” Sans asked. Undyne’s red ponytail shook back and forth with her back still turned to him. The skeleton sighed, discouraged.
A squawk of delight made Sans jump. Undyne was digging through the refrigerator. She emerged from it and victoriously presented Sans with a muffin that was easily twice his size.
“You like blueberries, r-right?” Undyne set the muffin on the counter next to Sans. His wide eyes seemed to sparkle as he approached the huge confection.
“INDEED! Thank you for your most generous offer, Dr. Undyne!” The skeleton smiled brightly up at the aquatic monster. Undyne’s blush went unnoticed as Sans tucked in. Sans was a very cute skeleton to begin with. Now that he was the size of a muffin, Sans was beyond adorable!
Sans broke off pieces of muffin with his miniscule phalanges, leaving crumbs scattered around him. Each bite that he brought to his mouth made him feel more energized. The pouch of blue magic that rested in his abdominal cavity below his ribs steadily expanded. The fullness of his stomach always comforted Sans. When he was full, he was safe and happy.
About halfway through the muffin, Sans’ pace slowed. He wasn’t hungry any more. But he knew that his tummy could grow to hold the rest of it. There was no longer a need to eat, but Sans still wanted more.
Undyne had been quietly watching Sans. It wasn’t everyday that she got to observe a skeleton monster eating. Although the most interesting process was covered by the makeshift bandana toga. The amount of food he ate was very impressive considering his current size.
A less scientific thing that Undyne observed was the endearing way the skeleton cheerfully munched his handfuls of muffin. She hadn’t wanted to interrupt his meal, but she noticed a definite belly bulge beneath the bandana and Sans was eating much more slowly. Surely he was full by now and just didn’t want to seem rude by not eating it all.
“I-if you want, I can setup some anime for you to watch? And you can keep the rest of the muffin for a snack?” Undyne suggested.
Sans stared longingly at the other half of the muffin. He wanted to eat it right now. But he would polite and show some self restraint. “That sounds like fun! Can we watch the one with the robots?”
~
Sans groaned pitifully and held his aching stomach. Anime played on the monitor that he lay in front of. Undyne had gone to check on her experiments some time ago, leaving Sans alone with his muffin.
The colorful animation had held the skeleton’s attention for awhile. But soon he was tired of craning his neck to watch the tall screen. With his one distraction exhausted, his self restraint hadn’t lasted long.
He had slowly pushed morsels of muffin into his mouth, enjoying the stretch of his magic as it grew. The blueberries left faint blue stains on his jaw bone. His blue belly was firm and swollen by the time Sans had realized that the muffin was gone.
“Gollie! I ate it all. Truly, there is no obstacle too great for the Sensational Sans. No matter my size!” Sans declared. He raised his hand to attempt a dramatic pose, but the sudden motion upset his stomach. There was an uncomfortable bubbly sensation that traveled up to his mouth.
“MUUURP.” Sans let out a loud burp. He looked around frantically to make sure no one had seen him. He laid down, ashamed of his vulgarity. His boney hands patted the round distended ball of magic soothingly.
“Sans? Are you o-okay? I thought I heard something?” Undyne walked back into the room, curiously searching for the source of the strange noise. Sans felt another buildup of pressure trying to force its way out. He gritted his teeth and held it in. He tried to grin, willing Undyne to leave quickly.
“Sans? Is everything alright?” Undyne stared at him. Sans nodded. Undyne looked unconvinced.
“Why aren’t you talking? O-oh no! D-did you lose your voice?! I’m going to call Alphys. What will I tell Papy-”
“UURRRPPP.” Sans belched. He covered his mouth with both of his hands. His bones trembled in mortification.
Undyne’s glasses slid down as she looked disbelievingly at the small skeleton. Did he just burp? How could a skeleton even do that?! Was this a side effect of the Shrinking Sauce? Had it interacted badly with the muffin? Now that she thought about it, where was the rest of muffin? It was gone, only the paper wrapper remained.
“Did you eat the entire muffin?” Undyne asked in awe. Sans grimaced guiltily. His stomach gurgled and he reached down to stroke it.
“Sorry for my rudeness. My stomach is struggling to overcome a deceptively difficult opponent.” Sans whimpered. Undyne took a moment to translate in her head.
“S-so, you have a bellyache? Can I help?” Undyne watched as Sans’ tiny hands moved over the bulge that must be his stomach. She had an idea. Slowly, she picked Sans up, cradling him in her scaly hand. Her thumb hovered hesitantly above his tummy.
“Is this okay?” Undyne couldn’t tell what Sans was thinking, but with a bashful nod of his skull, he gave her permission to rub his belly. His cheekbones blushed blue to match Undyne’s skin as she massaged him gently with her thumb.
Sans couldn’t help sighing and moaning in relief as Undyne applied steady warm pressure to his engorged magic middle. It felt much better when another monster rubbed the pain away. Undyne was flushed, but she continued to pet the taut surface of Sans’ magic.
Just when both of them had relaxed into the peacefulness of the moment, an alarm blared. Undyne yelped and dropped Sans into her lab coat pocket without thinking. She ran to see what had gone wrong in another part of the lab.
Sans was jostled about in her pocket. He couldn’t gain any stability. The constant shaking as he bounced against Undyne’s side made him feel queasy. The magic inside of him felt like it was going to explode.
His cry of distress alerted Undyne to the situation. But she had to concentrate on fixing her experiment. She compromised by sticking a hand in her pocket to comfort the tiny monster. Her fingers resumed their even warm strokes.
Sans mewled. His bones had stiffened in discomfort. However, Undyne’s fingers sapped the tension out of him. His stomach settled under her ministrations.
It was dark and warm in Undyne’s pocket. When he yawned, his jawbone almost unhinged. It had been a very long day. His eye sockets drifted shut and the small skeleton fell soundly asleep.