Flowey Is Not A Good Life Coach by unrestedjade has been killing me and this resulted from their story on AO3. It can be read as a standalone but makes less sense that way. I may or may not add more...
I really wanted to play with monster physiology and theoretical medical practice and sappy whump. I am sorry.
[sans]
It was a race against time to stabilize Papyrus after that. Undyne had helped Sans get him settled atop a few towels on his bed, Grillby standing in the corner of the room and acting as a living furnace while Gerson tended to the young skeleton's wounds.
"These are going to scar," the old turtle had said. He'd been filling some of the heavier cracks he couldn't heal with an amalgam made of crushed bits of bone Sans had donated personally and a specially prepared collagen formula.
"I don't care as long as he'll be okay," Sans had told him. The entire time he'd held Papyrus' hand in his, gripping it like he needed the lifeline.
After, they'd wrapped up the younger's remaining wounds and set him in his own bed, covered in a mountain of blankets. Alphys had arrived and set to work immediately on installing a heater for the brothers. Gerson provided Sans with a bowl of melting snow and a cloth, instructing him to keep it cool and pressed against his brother's brow until the fever broke. A few others had helped insure that the house become updated with the proper insulation so both temperature and pressure could be held with relative reliability. Sans, though with some hesitancy, had agreed to teleport people in and out of the house too.
Ideally they would put Papyrus in an incubation tube where he could be closely monitored in suspended animation and his environment properly controlled but Alphys didn't have what she needed to get any of the old ones functional again.
That left the royal scientist and her small reclusive team fortifying the skeleton household with the appropriate accommodations Papyrus would need.
Undyne had been told to go home after her hovering had almost pulled an electrode taped into the crook of the Pap's arm out. Very reluctantly she had done so and only after Gerson had promised to call her if anything happened. Grillby was next to go, not wanting to cause any trouble with the heater now installed and needing to get back to his family in the hotlands. Alphys and a few others had then taken off, needing to come up with a way of feeding Papyrus the right amount of nutrition and mana. Sans agreed to let her use his lab should she need it.
Gerson would spend the next few days at the house to provide regular healing therapy for the young skeleton and ensure that Sans was taken care of- seeing that the elder wasn't about to become unglued anytime soon.
Now, in the early morning the day after the attack, the skeletons were left alone together, listening to the wheezy snores of the old tortoise in the neighboring room. Tucked into the upper right hand corner of his brother's bed Sans watched him sleep with his hood drawn over his head.
The bags under Papyrus' eyes hurt just to look at and it seemed that every breath he braved to take caused another cough, bones shuddering under the blankets. He looked so brittle, so like chalk, as if Sans was too forceful he'd chip away in his hands. Pap's bones looked grey and tiny little craze lines formed scratches across his face and arms.
Trying futilely to swallow the thick lump in his throat Sans lifted the cloth from his brother's brow and dipped it into the bowel. The gentle trickle of water being strained reminded him of glass. Unbothered by the cold trying to bite into his hands he gently lay the freshly soaked fabric across Papyrus' forehead again.
His hand rested where it was for a moment before sliding back and over the crown of his little brother's head. With great care he rubbed his thumb back and forth, watching his expression carefully for any sign of discomfort. But Papyrus' expression was entirely at ease- expressionless, blank, refusing to let Sans in.
A deeply pained, fragmented gasp fluttered into his nonexistent lungs and he choked out, "I-I'm so so-rry, Papyrus." He folded forwards, pain drawn tight into his face like this was the most excruciating thing he'd ever experienced. Watching his brother die slowly and painfully was impossibly worse than holding his ashes.
Brow to brow Sans closed his eyes and held his little brother, his whole world, his home, his reason for living, in his hands and begged whatever higher deity was out there not to take him away again oh god please I can't take this anymore leave him alone yousadsickbastardshedidn'tdoanythingtodeservethis!
Oh geeze, he was crying now. The pressure in his chest crested and soft, terribly painful sobs broke through him with such force that he was left hiccupping. Sans curled himself around Papyrus' head, holding him as tightly as he dared, cherishing the gentle push of breath that tickled the side of his neck and jaw.
"P-Pap-" the words felt like thorns in his throat, whispered so quietly and yet still like sandpaper against his metaphorical windpipe, "stay… Oh god, please stay." His body shuddered through another harsh sob, tears squeezed out of his clenched eyes. Several beats of silence passed before he could speak again, running his thumbs over Papyrus's temporal bones. Opening his eyes and looking down at his prone little brother Sans whimpered, "I c-can be happ-y anywhere so long as you're there to-too, bro." His voice was thick and quavered, "I'll do whatever you want- we'll go wherever you want. Just please stay," he swallowed again, trying not to choke, "you're my home, Papyrus. The w-world's not worth living in when you're not in it. I am begging you; stay with me."
He sniffled and hiccupped loudly, trying to fight the tears and failing. Papyrus twitched when he moved away, unsettled by the loss of contact, and breathed deeply. Sans returned to his earlier ministrations, gently petting the side of his little brother's head.
"I've got you, lil' skell," he whispered, "and I won't give up if you won't."