I'm not really sure what my plan was here, but backstory. Sans is the most powerful monster in the underground, he's tall and strong. Papyrus is pretty small and weak. No magic attacks. This is after Chara but before Frisk falls down.
"Yo Paps, Undyne's here, you coming out?"
Sans stood at the door, shouting up the landing. Papyrus wasn't up yet and Undyne had come to ask if he was coming to their lesson today.
"Has he even got up today?" Undyne asked, tilting her head back to speak to Sans, who, in true laziness, was levitating a ketchup bottle to his mouth and sucking from it slowly.
Sans sighed and unlit his eyes, catching the bottle as it fell from its blue cloud.
"I haven't seen him yet, I figured you wore him out yesterday trying to get him to find his magic"
"No, he shouldn't be that tired, I didn't go that hard on him!" Undyne replied, defensive yet worried she'd hurt poor Papyrus. She knew in her soul he didn't have copious magic like his brother, but thought there might just be a trace he could use.
"He might just be feeling down about not succeeding, I'll go check on him and send him over, don't worry. I'm sure he'll gill over it soon" He said, catching Undyne's worry. She glared for the pun, but nodded and headed off to see if Alphys was around for some more history lessons.
Sans plodded upstairs, sucking thoughtfully on his ketchup bottle, wondering how best to cheer Papy up about his lack of magic.
"Knock knock, are there any lazybones in there?" Sans called out through the door, waiting for a tell-tale groan from his brother, but instead
"Go away Sans, I'm not in the mood" came a hoarse voice from behind the door.
Sans tried the door handle, but it was locked (which was odd as Papyrus never locked his door or the bathroom door for that matter, like ever. That had led to a few awkward walk in scenarios when Paps was changing). Sans stalled, mulling over what to do. Either he walks away or try to get in, respect Papyrus' wishes but leave him feeling bad, or push…
"Alright, I'm gonna leave you alone for an hour but then it's dinner time and you promised me the new spaghetti recipe Undyne taught you."
Sans wandered off to his room, hands in his hoodie pockets. He walked over to his bed, using his magic to shift the clothes off without even thinking and lay down, musing what he could do.
He'd always know Papyrus wasn't as magically adept as he was, ever since he was younger. When Gaster had been around he'd always taken more interest in him, although at the time he couldn't figure out why. Papyrus was older and in his head that had meant stronger. That was till things in the lab blew up, almost literally. It had been second nature to Sans to shield himself from the debris and flames with magic, he could still feel the panic he'd felt when he saw Papyrus helpless, trapped under debris, no sign off magic, not even a flicker of an eye glow. He'd rushed back to save him, pushing his young magic to the limit and shielding them both. That's when he knew his brother was unlike him. Papyrus was normal, Sans was, as Gaster would say, exceptional. They never saw Gaster again, he'd been trying to save something, some machine when he disappeared in flashes of lights and flames. Sans didn't really care, Gaster was blasé about Papyrus and pushed Sans too hard.
It had taken Papyrus a few weeks to recover, Sans may have been young then, but he knew he had to step up and do something. He managed to get a cushy house with funds he'd repurposed from the now missing W.D Gasters account. As Papyrus recovered, they fell into a natural way of Sans taking care of Papyrus, and almost everything else. It really was a blessing that Undyne came around and offered Papyrus Royal Guard training, it had been doing his so much good (even if he wasn't necessarily fighting, more feeding). Papyrus felt useful and capable and Sans knew that. That was until Asgore brought in compulsory magic training due to the threat of more humans falling in. Undyne had tried to get Papyrus hyped and in touch with his, but there just wasn't any there. That crushed Papyrus, he could never be in the guard officially.
Sans stretched and sighed. He'd warned Undyne about not pushing it, the physical signs were all there. Papyrus was pretty small and weedy without much soul glow, but she'd insisted that someone with so bold a personality must at least have some form of soul energy they could harness, even just by redirecting others power. But the results of the last session came up with nothing. She'd exhausted herself trying to redirect through Papyrus, and he'd stalked straight off to bed when he came back.
Sans checked the clock, it had been about an hour, he decided to try again.
He wandered over and knocked 1, 2, 3 times. No response. Maybe he was in the kitchen? Sans listened out but there was no noise downstairs. He sighed again, audibly, and clicked his fingers. Papyrus's door clicked open with a flash of blue and he wandered in.
"Yo Paps, you can't stay in bed all day, that's my…"
Sans stuttered to a stop, taking in the sight. The room was a tip. Figurines on the floor, desk pulled over, as if someone had thrown themselves around the room in anger?
Or agony. Papyrus lay dangling off half the bed, half undressed and trembling. His bones had turned grey instead of their stark white. Sans rushed to his side, scooping him up, feeling the outer layer of his bones crumble, turning to dust on contact. Dust was everywhere, bed sheets, clothes. Papyrus was crumbling slowly.
"Papyrus?! Can you hear me? Look at me, tell me what's happened!"
Papyrus coughed, the movement causing dust to rise on his bones. His voice was even hoarser than an hour ago.
"Sans, I don't think I'm very well"
"No shit, we gotta get you to Alphys, she has to know what to do!"
Papyrus tried to struggle, protesting "No, the wind, it'll make me worse, please"
"Fuck that" Sans replied, focusing briefly and appearing in Alphys' lab.
"S s s sans! What's going on?!" Alphys shrieked, jumping up from what seemed like underneath Undyne, Undyne leaping up from the coach looking decidedly flushed.
"It's Papyrus, he's crumbling, I can't do anything, help!" Sans practically shouted at the poor scientist.
Sans was right though, Papyrus was looking weaker for the jump, more dust on Sans' body then bones on Papyrus. Alphys, too flustered for words ran to the lab, Sans following, forming a barrier between Papyrus and the slight air movement that running caused in fear of losing more of his only family.
"Lay him down here, quickly" Alphys said, too focused to stutter now.
Sans lay Papyrus down on a small white table, as Alphys hurried to the controls and started scanning and testing.
"You need to scoop some dust into a test tube for me, I need to see what's happening to his DNA and I'm not risking taking a sample from his soul now."
Sans used a small brush and tube handed to him, and gently scrapped some of Papyrus' remain into it.
"Can you stabilise him Alphys? Please?" Sans begged, tears starting to stream on his face, eyes flicking from the reading to papyrus to Alphys.
"I'm going to lock the pod down and feed everything I can that normally sustains Skeletons into it, I'm trying Sans" Alphys said, not looking up.
Sans wasn't rational though. As the stasis pod closed, he started to panic.
"Alphys you gotta do something, I can't lose him, ok?!" Sans said, towering over the small creature. It's hard to not intimidate when you're over 3 times as tall as someone…
"Hey Sans back off her, she's gonna do her best and you should leave her do it, ok?" Undyne said, finally composing herself and defusing the situation. "Papyrus is in stasis, he can't get worse, we're gonna do everything we can, I already called Asgore to see if we can use the stored Magic to keep him going for as long as we need till we can cure him, he said yes, now come sit down."
Sans took a deep breath and tried to calm himself, Alphys was trying to remain composed but had tears prickling and needed space to work, he knew this.
"Fine, ok, you're right" he looked back at Papyrus, now suspended, with various shimmering gases moving in the pod to sustain his fragile body for as long as they needed.
"Sorry Alphys, thanks." He said, trailing off, moping out the room after Undyne.
He flumped on the sofa, the soft hiss of the lab door shutting after him sealing Papyrus away till Alphys called them back.
Undyne sat across from him, clearing up some empty noodle packets and general rubbish, and then finding that the bin was full anyway, lay back on the sofa. Neither of them wanted to say anything for a while, even if they did what was there to say? Sans slowly slumped lower, till he was practically half his height in the seat, racking his brain for a cause.
His eyes flicked to Undyne regularly, something slowly forming. The last thing Papyrus had done was redirect Undyne's magic, the only thing out the ordinary for him was that. Could she have hurt him? Damaged him enough to kill him, slowly?
He started to grind his jaw, she'd promised to go easy, that she'd done it so many times before, that it was safe, even if someone had no magic, at the levels they were using the only damage they'd receive was similar to knocks and bumps. But then Undyne had been known to be over confident, had she lied to Sans?
"Stop it Sans" came a harsh snap from across the room. Sans sat up and looked around, shocked.
Without realising he'd called hoards of bones and blasters around him, all targeting Undyne. She herself had called her spear and shield up, glaring at him from over it. Sans unclenched his fists and shook his body. The magical tension in the room lowered considerably, and the eerie blue glow faded along with it.
"Don't think I'm not thinking it too. Did I hurt Papyrus? I didn't think I'd even scratched his HP levels, I didn't even graze his soul for damns sake. But now we're here and he's there and something has damaged him so, so bad. I can't, I couldn't live with myself if anything happens to him, I'm so sorry Sans!" Undyne burst out into sobs, spear fading, curling into a ball and shaking.
Sans didn't know what to do, he still thought it was her, he couldn't absolve her guilt, but he could comfort her. He called some soft blue energy and slowly pulled her up and next to him. Wrapping his long body around her, he held her and started to cry too. They sat and cried till they couldn't shed another tear, slowly slipping in to a more comfortable silence.
