.

Not with a Bang but with

Author's Introduction: (There's a fair bit to say before we begin so bear with me, but if you'd rather scroll down and skip the author's note, still maybe check in on the trigger warnings because, uh, there's a lot of those).
Wowie! This is going to be a big one, a really big one. I cannot tell you how excited I am to finally get this story out, as it is the result of nearly five months of hard outlining work, and now it's finally ready to share.

This story is set in a True Pacifist ending, and no run has been completed before. My Frisk is a Pacifist and always will be.

In this story, Frisk will also be portrayed as a girl. Please try to keep an open mind and remember Frisk's gender is up to the player. I mean no disrespect or ignorance to nonbinary individuals and the LGBTQ community, and Frisk's gender bears no significance to the plot of this fic, just like it bears no significance in the game. You can in your head read Frisk as nonbinary or male if you want to in your head, and if using alternate pronouns in the reviews makes you feel more comfortable, then feel free. That being said, I mean to continue using female pronouns for Frisk, if only within the context of this fic. Thank you.

The story's gorgeous cover art was done by tyl95 on deviantART; coming from his comic "The River's Warning," and is being used with permission.

This story also draws inspiration from some Undertale authors vastly superior to me – mainly, Zarla's Handplates comics, but also some from ABadTime's BOTWOT and talkingsoup's phenomenal The Scientist series, all of which are works you should definitely check out.

Trigger warnings: There are a lot of these – this is one dark story, so specific warnings will be posted on individual chapters, but main/general ones to look out for are violence, body horror, inferences to depression/alcoholism/suicide, and child abuse/experimentation/torture, as well as occasional cussing.

For my own reference: 16th fanfiction, 4th story for Undertale.

CHAPTER ONE:
The Hope for All Monsters

Specific trigger warnings on this chapter for child experimentation and child abuse.

oOo

When Sans was seven, he got a little brother.

oOo

Tap-tap. Tap-tap-tap.

Twitch, twitch.

Tap. Tap-tap-tap-tap-tap.

Twitch, twitch. Kick.

Tap-tap. Tap –

"Stop that."

Sans drew his forehead away from where it had been pressed to the Plexiglas tube and reluctantly let his hand drop to his side. After taking in the long, expectant look, Sans back-pedalled a few steps.

"But I like it when he twitches like that."

"He's not alive yet."

"Yeah, that's what you say. But how come he keeps twitching then if he ain't alive?"

"Isn't."

"Whatever."

"Isn't."

"… isn't alive."

"It's a reflex, a simple physical spasm. He won't be ready for a few more weeks."

"How many weeks?"

"Until the body is strong enough to be removed from the solution, at which point the soul can be safely kindled from the dormant state it's in right now. It was the same with you, you know."

"Oh. But, how many?"

Sigh. "Six or seven."

Sans eyed the new skeleton with fascination. He wanted to go up near the tube again. The new skeleton looked so still, just floating there in the blue and green magic-based solution. If he didn't kick every once in a while Sans worried he was dead. "… why are you making him again?"

"That's my business, not yours."

"But you always answer my questions! Always! And you said you always would! You said!"

"So long as they concern you, yes. This doesn't."

Sans backed down, staring at his feet. He chewed on the sleeve of his oversized sweater. "Are you gonna get rid of me after?"

"That's ridiculous, Sans. Where in the Underground did you get that idea?"

"I dunno. 'cause you made him after you messed up with me, and maybe you don't want me anymore. Like maybe… you want someone new." Sans lifted a hand self-consciously to his right eye socket, prodding at the bandage. It was itchy. He hated the bandage. It was stupid. He didn't get why he had to keep wearing it – and for a whole entire week more, too, even though the accident had happened ages ago. That stuff he'd been told about having to shield it Just in Case of Side Effects was stupid, too. It wasn't like it mattered if there were Side Effects in his right eye anymore, anyway, seeing as it was useless now. Ha-ha.

"Stop that."

He'd been tugging at the bandage again. Sans stuffed his hands into his pockets. "Sorry."

"I am not going to 'get rid' of you, Sans. But yes, after your… accident, having two of you will probably be for the better, and more efficient besides. It'll be a year before I'll really be able to start working with him anyway, just like I had to wait a year with you."

Sans jumped when he suddenly felt a hand on his right shoulder, not having been able to see it coming, then his breathing evened out again. As much as it ever did with physical contact, anyway.

"Why don't you head on home? You can watch television until I get back, if you like. We're done for today."

Sans sighed, but began to make his way out of the room. He cast a glance over his shoulder at the new skeleton on his way, however, and stopped. "We're gonna get to know each other, though, right? Like, you're not gonna keep one of us shut up down here. I'll get to… grow up with him and stuff?"

"Raising you separately would only overcomplicate things, yes."

"So he'd be like… my brother?"

"… if you like. Now go. I still have things to do down here. You should probably make yourself something to eat."

Sans went, making his careful way through the basement lab and to the elevator – navigating without depth perception still took some getting used to, though he was steadily improving. By the end of the week, he'd be able to return to school. And perfect timing, too – the other children would inevitably have ended up laughing at him over the bandage, and he already spent enough time out of school to be appropriately estranged from them as it was.

He had cereal for dinner, left the dirty bowl on the table, then headed up to his room to read his comic books. He heard the front door open and shut downstairs, but he was left undisturbed. He was usually left undisturbed, especially these days.

But at midnight, he snuck out of the house via his bedroom window, trotting through the streets of New Home all the way to the lower labs, where he made a beeline for the Plexiglas tube. Alone, he tapped as much as he wanted, and the new skeleton – his brother – twitched and kicked away.

oOo

The new skeleton came out of its tube while Sans was at school. Or, more accurately, while Sans was skipping school, out in the main caverns of Waterfall. He'd been skipping school more and more often lately, and his grades weren't very good. Well. Except for math.

Sans was really good at math.

But he hated school. He hated the teachers who cast him strange, pitying looks when they thought he wasn't paying attention. He hated the other kids, who ignored him and excluded him from their games, and who were all so painfully stupid they made Sans want to bash his skull against his desk until he dusted. He hated the schoolwork, which was either too easy or too boring or both. Gaster never kept a terribly close eye on him, and taking the ferry over to Waterfall instead of walking to the New Home school wasn't much of a task.

He liked Waterfall, liked the stones that glinted in the cave ceiling. He knew it like the back of his hand. Though the glittering stones could be found in most of the rooms along Waterfall's main road, there were countless other little caves and grottos jutting off the road, which led to countless more little caves and grottos, and then there were other caverns that were so small and hidden only children could have explored them, or even known of their existence.

It was these little rooms Sans favoured. He could sit or lie down on the muddy cave floor for hours, just watching the glinting stones. They gave him a sense that there was really something out there, something beyond the Underground and beyond Gaster. They were something that belonged to him and him alone. Nobody could find him in these caves.

When he got home, around the same time he would have done if he'd actually gone to school, the house was still. Quiet. Almost dead.

Sans set his schoolbag down by the door and looked around. Gaster hadn't told him to report down to the lower labs, had he? He was sure he hadn't. Maybe he was just doing paperwork, or monitoring the new skeleton.

The child faltered before venturing further into the house, peering into the kitchen. Empty. He was turning back to the living room when a voice at the top of the stairs made him jump.

"Come upstairs. Quietly, now."

Sans looked up at Gaster in suspicion. He was standing at the top of the stairs, seemingly expectantly. He was still in his lab coat. "Why?"

"Quietly, I said. Now, come upstairs."

His soul fluttered anxiously in his ribcage, thrumming a nervous rhythm like a skittish rabbit's. Had someone from the school come to tell Gaster that he was hardly ever there? Had someone come about that time he'd been sent to the principal's office for talking back to his teacher in History class? Was Gaster going to lock him in the closet again for the night?

But still, he went, reaching up to grip the banister. As he approached the top of the stairs, Gaster turned on his heel and vanished into Sans' bedroom. Sans followed.

At first glance, nothing seemed terribly amiss: his "posters," pages torn from textbooks and encyclopaedias about physics or what they called "astronomy" on the Surface, were still taped crookedly to the walls. His curtains were still drawn, as Gaster always made him draw them shut. His bed was still unmade, his teddy bear resting on top of his pillow where he always left it. His desk was still a scattered mess of papers and pencils and crayons and books. But his comic books had been neatly stacked in one corner, and his toys had been stashed away somewhere from where they'd been strewn across the carpet. And, lying in the middle of the floor, was an unfamiliar large basket. Gaster was kneeling by it.

Sans, who had stopped in the doorway, frowned and stared. "Is that… uh, a new thing?"

Gaster snorted at that. "If you like. Come. I removed the new skeleton from the solution this morning. He is ready."

All apprehension forgotten, Sans bolted forward and threw himself to his knees by the basket's side. "Really? Is he really? Can I see?"

There was no response. Gaster reached into the basket and pulled out a bundle of blankets barely bigger than Sans' teddy bear. Sans scrabbled over to get a better view, his eyes wide. There, swaddled in pale green blankets he recognised from the lab, was a skeleton. The same skeleton Sans had watched floating in the tube for nearly six months, only now it – he! – was out of the solution and he was alive. It was a living skeleton with a soul, just like him, but tiny. Sans had never realised just how small the new skeleton was until now.

"… whoa," was all he could say.

"Hmm. Yes. He is larger than most newborns – while in the tube, his growth was accelerated – far too many risks involved if he'd been removed before, not to mention all the unnecessary fuss. He is about the size of a three-month-old infant, and his intellectual capacity should catch up relatively quickly – that is one benefit of the solution. You caught up even quicker than I expected you to yourself. I remember it well. Perhaps it will be the same with this one." There was a pause. "… I suppose you'd like to hold him?"

Sans' head bobbed vigorously up and down, holding out his arms. Gaster had taught him how you were supposed to hold babies ages ago.

The skeleton had been sleeping, but as Gaster placed him carefully in Sans' arms, he blinked open his eye sockets. Tiny fists opened and closed. He made a little cooing noise. Sans cradled him close and carefully, just as he'd been taught. The new skeleton yawned widely, and Sans broke into a grin, running a finger along the baby's cheekbone.

"Heya."

The new skeleton made more cooing noises.

Sans addressed Gaster. "What's his font? Or do you not know yet, 'cause he's just – "

"Oh, I know his font, certainly. You should have heard him when he woke up. Bawling louder than any skeleton I've seen in all my life. It was not difficult to determine his font."

Sans didn't even look up, too focused on the new skeleton, on his brother. "What was it?"

"His font, you mean? Papyrus."

"Papyrus," Sans mumbled to himself, only tripping over the name a little. "Hey, Papyrus. I'm your big brother." He stroked the baby's – Papyrus' sternum – and a new feeling was kindled in his soul. Something almost warm, warming, the feeling swelling to spread through his bones, through his very marrow, until it filled his entire body and he could feel nothing else.

For here was a creature, tiny, innocent, and defenceless, and whose creator was the same as his own. And he was holding it, holding him, and he was blinking up at Sans without fear. A creature who didn't know what it was like to be locked in the closet for being bad, who didn't know what it was like to have to be strapped down on the examination table and get injected with all manner of things that made him sick, or face strange and intimidating machinery. His brother.

His baby brother, who didn't know how scary it could all be.

His. Brother.

His.

And holding him, all Sans could think, all Sans could feel, was an overwhelming desire to look after him, to teach him all that he knew, and to protect him, and make sure he never, ever hurt. He smiled down at his brother, and his brother was – he was, he was sort of smiling back - and he was his.

When Sans finally looked up, Gaster had left the room.

oOo

Six Months Later

oOo

Gaster came for him in the early evening, when Sans was in his bedroom. He was playing with Papyrus, sat outside his brother's crib and showing him the flash cards he'd made to teach him the shapes. He knew Papyrus was too little to make anything more than babbling noises yet, but he also knew his brother was smart, and he picked up on things fast.

Now the baby bounced happily where he stood, gripping the bars of his crib to hold himself steady.

"Circle," Sans said, grinning and holding up the appropriate card. "Circle."

"BAH!" Papyrus replied, and he giggled, apparently pleased with himself.

"Circle."

"Bah." Papyrus, having lost interest, promptly dropped onto his bottom and began to play with his toes.

Sans sighed and tossed the cards aside, scooting closer to the crib and leaning over the top of it to stroke Papyrus' skull.

There was a knock at the door, and Sans jumped and spun on the spot. Gaster was standing, hands folded behind his back.

"Sans. With me."

Sans scowled. "What for? It's gonna be Papyrus' bedtime soon."

"Sans."

"But Papyrus – "

"Now." He fixed him with a look that chilled him to the marrow.

There was a pause, and Sans nodded. He reached into the crib a moment and picked up Papyrus by the armpits. "See ya later, baby bones. Sleep tight." He clicked his teeth against his brother's skull before setting him back down and making his way out. Gaster, meanwhile, turned on his heel and strode back into the hall and down the stairs.

Sans looked over his shoulder one last time at Papyrus. His brother's attention was wholly focused on gnawing at a teething toy that Sans was pretty sure was intended for dogs. He'd be okay.

It's just a regular old experiment. You don't gotta be so scared and act like a baby bones, he reprimanded himself.

Sans shut the door to their shared bedroom and went to meet Gaster, but he paused at the foot of the stairs. Lingering. He glanced over his shoulder once more when he felt a sudden familiar heaviness weigh on his soul. He didn't need to look down at his chest to confirm his soul had been turned blue. Although he was prepared for it, he stumbled as Gaster tugged him sharply forward, short legs struggling to keep up with the scientist's long strides as he was lead out the door and through the streets of New Home in the direction of the lower labs.

When they got to the elevator, Sans dared to speak. He was nervous, yes, but anything was better than waiting in apprehension, in Gaster's cold silence. "So, uh. You gonna tell me what we're doing today?"

Gaster slid his gaze Sans' way, and the child shifted slightly. There was a pause, weighed down by its lengthiness, then: "The Determination solution is ready."

Sans had been looking down at his sock feet; now his gaze snapped up. Gaster sounded more excited than Sans had ever heard him. Not that Gaster ever betrayed excitement at all. Or much of any emotion, really. "The… "

"Yes, Sans." A ding, and the doors to the elevator slid open. "Do you recall the studies I've been working on?"

"Kinda." Sans stumbled as he felt Gaster give a sharp tug on his soul again. "You said Determination, uh, DT, is linked to the abilities of Saving and Resetting? And, uh, that only beings that can, can do that, are, um… um… "

"Only beings with high, concentrated amounts of Determination have the ability to Save and Reset, yes." Gaster's footsteps clicked on the tiled floor, echoing off the lab's high ceiling. "And therefore have the ability to manipulate the timeline. Beings with such an ability are what we call…"

"Anomalies," Sans recited dutifully.

"Indeed," was all Gaster said. "And only humans have enough Determination. Hence why I have been hard at work studying the souls of the humans who have, thus far, fallen into the Underground. Unfortunately none of the fallen souls have sufficient Determination that they have the abilities of Save and Reset. Not yet, anyway. We only have five at the moment. Those souls prove inferior subjects of study regardless – Determination is needed to manipulate the timeline, but seems a key component in prematurely shattering the Barrier as well."

Sans paused. "Did you determine that?"

Gaster ignored him. "Despite that. The souls all have at least some Determination, as all humans do. Children especially, it would seem, and it certainly helps that the oldest of the humans was but twelve. And each of the five human souls has varying amounts of Determination, varying usefulness. Green? Not terribly Determined. Orange, however… "

"Because orange and red are on the same colour spec-trum," Sans piped up.

There was a pause. "Yes. Very good, Sans."

Sans brightened a little, then a new tightness gripped at his soul. The lower labs were enormous, he knew, spreading below much of Hotland and a decently-sized portion of the capital as well. They formed a complex labyrinth of corridors only a fraction of which Sans had actually seen. He now realised that Gaster had led him to an unfamiliar part of the labs, and that unfamiliarity was making him feel very small.

As Gaster lead him into yet another unfamiliar corridor, Sans' steps slowed to a stop. The room they were in was huge, larger than any Sans had visited before. From the ceiling loomed a machine, great and imposing and over three times Sans' size. It reminded him of an animal skull – of Gaster's blaster attacks, specifically, which he liked to call Gaster Blasters because the rhyme made him giggle – complete with a bifurcated jaw and two gaping holes like eye sockets. Thick wires curled from the machine's top into the ceiling and out of sight, as if it were just a part of some much greater, even more intimidating creature whose head was peeking out from around a corner.

"…. What's that?" Sans heard himself whisper.

"Ah, that's right, you haven't had the honour of seeing it yet, have you?" Gaster stopped before the machine, placing a hand against one of its curling mandibles as if stroking the muzzle of a beloved pet. A fond smile flickered across his face. "I finished working on this old thing just a little after you came out of your tube. I have been examining the human souls ever since, trying to discover the best way to put the Determination to use, pouring over my blueprints for more sleepless nights than I care to recall."

Sans barely heard him, unable to tear his gaze away from the machine. He realised, dimly, that he was trembling, and this time the tug on his soul took him by surprise. He nearly fell to the ground tripping over his own feet.

"Come on."

Gaster led him past the room and through another few corridors, then, finally, into an enclosed room. It took Sans a moment to place it as the examination room in which Gaster performed most of his experiments, and he wondered whether it was in fact the same room, and that they'd taken a detour through the labs, or if Gaster had many of these rooms spread throughout the labs, all of them identical to one another.

It probably didn't matter, anyway.

Yet still – it was familiar, and Sans took comfort in that. In the middle of the room was a metal examination table, and to the side of the examination table was a small tray table on wheels. Familiar pieces of medical equipment were already laid out upon it – syringe, scalpel, bottle of disinfectant. The far side of the room housed a desk with a computer, and a series of machines and strange equipment, most of which Sans had no names for.

Those machines had always been scary-looking to Sans, but they were nothing next to the Determination Extractor.

"Shirt off," Gaster said, waving a hand as he dropped into his desk chair. He let go of his grip on Sans' soul, but Sans didn't feel any lighter. He pulled off his sweater and T-shirt and bundled them up before tossing them into a corner and climbing up onto the examination table without being asked.

There was only a very short pause before Gaster summoned his magic hands, and Sans lay still and flat on his back as the hands fastened the table's straps around his wrists, ankles, waist, and forehead. The straps kept him even from squirming very much, but he could arch his spine to try and get a look of what Gaster was doing from his limited vision. From what little he could see, the scientist was in the process of doing something with a syringe – filling it, he figured – as some files ran on the computer. Meanwhile, the magic hands fastened a series of electrodes to Sans' skull.

Sans swallowed, closed his eyes, and tried to relax.

"Sans." His eyes snapped open again to see Gaster standing over him, holding a syringe filled with… something. Something red, a bit viscous. Sans had never seen blood before, but he supposed it must look a little like that. "Have you gathered what it is we're going to be doing today?"

"Um, not everything."

"Then allow me to explain. As we said, Determination is an ability and substance unique to humans, correct? Key to shattering the Barrier?"

"Yeah? What of it?"

"Now, Determination is an incredibly powerful substance. Truly, its potency goes beyond words. So powerful, in fact, that pure Determination would doubtlessly destroy a monster's body. We are not a very strong species, after all." Sans waited for the usual reminder that he and his brother were not, in fact, monsters, not really, but it never came. "Combine the Determination with magic suited to a specific monster's body, however, just a tiny amount, and… well… " Gaster titled the syringe so that the light reflected off of it, almost contemplatively. "Even a little goes quite a long way."

If Sans had had lips, he would have licked them in his nervousness. "So that's – "

"Obviously. You are and always have been the vessel that will, one day, destroy the Barrier. I created you with that purpose in mind, and no other, as you know well. The machine extracts Determination from the human souls, but it serves no purpose beyond that. I have taken some Determination – a very, very small amount, from only one of the souls – and combined it with the kind of magic best suited to skeleton bodies. Over time, I expect, your body will develop a tolerance for it. By that point, the substance will have become a part of you, just as much as your bone marrow or your magic."

Sans kept his eyes on the syringe. "Lemme guess. If my body's gotta develop a tolerance for it, it's gonna hurt first, right?"

"Most likely, yes, I'm afraid."

"Hurt bad?"

Gaster ignored him, instead swiping his humerus with a cotton ball soaked in antiseptic. "Are you ready?"

Sans wasn't ready. Not by a long shot. Gaster had referred to the Determination Trials before, but he'd never paid very much attention. They sounded terrifying.

At some point, Gaster's magic hands had disappeared. Sans hadn't noticed.

Just shots, he reminded himself. Just regular old shots. No big deal.

He nodded.

A shuffle, and the needle went in with a slight sting.

For a moment, nothing. Sans almost let himself relax. Almost.

Then, in a heartbeat, it happened. Pain. Pain, burning pain, spreading through his small body fast as lightning.

And Sans screamed.

His spine arched. His fingers clenched against the edge of the examination table. His feet kicked desperately as much as they could given the restraints, and he screamed and screamed, eyes screwing tightly shut. He was dying, he was going to die, it hurt it hurt it felt like his very marrow had been set on fire he was going to die the pain was going to kill him and he screamed –

Blackness took over faster than he could ever have hoped for.

oOo

The sensation of being awake, washing over him slowly.

Something soft beneath him and on top of him. Warm, almost.

The hum of machinery, a thousand miles away. The feeling of being watched.

A strange, warm feeling in his sternum, and in his soul, a tingling sensation. Like something was waking up inside of him.

Dull pain and exhaustion, also distant, but fast approaching.

Alive. He was alive.

Darn it.

(Where had that thought come from?)

Still. He was definitely alive. No bones about it, heh.

Sans cracked open one eye, then the other.

He was lying in a bed in another part of the labs, in the infirmary. There was only one bed, of course, but Sans had been here before, on the few occasions he'd passed out, or an experiment made him so sick he was too weak to go home to his room straight away. He'd spent an entire week down here after his eye had been broken, he remembered. That felt like a terribly long time ago, now.

"Ah. Excellent. You're finally awake."

Sans startled, then turned his head. Gaster had been sitting on his right side, his chair positioned perfectly in his blind spot.

Still, Sans couldn't bring himself to do much more than groan and nod, raising a hand to his skull. Gaster studied him a moment.

"You must be very tired. That's all right. I've deemed you strong enough to walk, once you get your wits about you. You should be able to return to Papyrus. He has… missed you, I believe."

Painfully Sans pushed himself up into a sitting position. "Why? Was he okay without me to read him a bedtime story? How long was I asleep?"

A heavy pause. "Two days."

Sans nearly fell off the bed. "Two days?"

Gaster nodded. "Initially, your body reacted poorly to the solution, and you had to be stabilised."

"Oh."

"Hmm. Are you thirsty?"

Sans paused before realising that he was. His throat, such as it were, felt dry and rough. He nodded.

As if he'd already anticipated Sans' response, Gaster stood and walked over to a table on the far side of the room, where a water pitcher and an empty glass sat waiting. Gaster poured the water, then brought it over and passed it to Sans, who grasped it between his hands and gulped it down greedily.

"How do you feel?" asked Gaster once he'd drained the glass, eyeing him carefully.

"Still really sore. My head hurts."

"That is to be expected. But besides soreness, you feel fine?"

"I guess so… " Sans rubbed his humerus self-consciously, and realised Gaster had dressed him in a sleep T-shirt, though he was still wearing his old sweat pants and socks. "But I still feel pretty bad. 'm not real hungry… " He held back the whimper that threatened to escape between his teeth. "Can I go home now?"

"You feel strong enough?"

"Prob'ly." He didn't really, but he'd manage.

"All right then. Stand."

Sans climbed carefully from the bed. He felt dizzy, but he was steadier on his feet than he thought he'd be. Even after stepping away from the bed, he could stand without holding onto anything, and he only swayed a tiny bit.

A pause, silence stretched out taut between them, like an elastic band on the verge of snapping. Then Gaster waved a hand. "Very well, then. You can go. It's quite early in the morning; I doubt anyone will see you in the streets, and you're clever enough to think of a good lie regarding your condition if you do."

Sans nodded, but something held him in place. He hesitated. "Uh, Gaster?"

"Hmm?"

"You, uh, you… you said, uh… " Sans scratched nervously at his inner wrist. "You said my body, uh, didn't react too good to the Determination stuff, right? 'cause it hurt really bad."

"Yes, but it was to be expected, being introduced to a new substance, especially one such as Determination. But the short of it is that, yes, your body reacted quite poorly at first. That is correct."

"Did I almost die?"

"I stabilised you too soon for that to be a risk, but had I tarried, then you might have come much closer to death's door, yes."

Sans dared to be hopeful. "So the experiments are a failure then."

"Pardon me?"

"The experiments, they're a failure. My body reacted bad, so you ain't gonna do them anymore."

"No. I am."

Sans balked. "No?"

"No. After I stabilised you, your body absorbed the solution. The marrow I extracted from you, as well as the small layer of bone I took, showed excellent results. The Determination Trials will absolutely continue. They are most imperative, and you're being most unreasonable."

Sans paused. "Well, maybe I don't wanna do the dumb DT trials anymore."

"I beg your pardon?"

"I don't wanna."

"You refuse to cooperate?"

Sans paused, then stood a little straighter. "Yeah. Yeah, I do."

"Very well, then." Gaster turned his attention to his notes and his back to Sans, and the child's brow furrowed.

"Wait… for real?"

"Yes. You refuse to cooperate, then that's all good and well. The Determination Trials, however, are invaluable to my studies and to our endgame of destroying the Barrier. So if you refuse to be a subject, I shall simply have to turn to your brother instead."

Colour drained from Sans' face. "You can't."

"And why not?"

"You, you can't! He's just a little baby, you can't!"

"And yet, if you refuse, then you're telling me you'd rather he be subject. He is small, and may suffer far worse symptoms, but there is nothing to be done about it. We shall simply have to deal with any problems as they come."

Sans' hands balled into tiny fists. "You… you suck! Go inject your own dumb self with Determination and other weird stuff and see how bad it hurts! Go, go inject it up your butt! You're horrible! I hate you! You're a horrible scientist and I hate you!"

He cut himself off, breathing heavily.

The slap came out of nowhere, sending Sans' head snapping sharply to the left. He teetered on the spot from the sheer force of the blow, one hand raising up to cradle his stinging right cheekbone. Sans looked down at his toes a moment, and when at last he lifted his head, his small features were twisted into an expression of hatred, the embers of a cyan glow kindling in his good eye.

"You're not gonna hurt my brother."

Gaster's expression was nonchalant. "Are you going to be a willing subject and follow through with the Determination Trials, then? I only need one participant."

The crushing reality landed on him then. Him or his brother. It wasn't like there was a way out, and he'd been stupid to think otherwise. The glow in his eye sputtered, coughed, and died, until he was looking down at the ground again, tone dejected and eyelights gone dark. "… yeah."

"Excellent. No need to change our protocol, then. Now, if you consider yourself ready to return home to your brother, I suggest you do so."

oOo

Sans didn't encounter a soul on the walk home, something for which he was grateful. He was shaking so much his bones rattled. Getting out of the labs hadn't been too bad, but it was nearly half a mile's walk home, and Sans was starting to feel as if his legs could barely support his weight. It didn't help that he was still aching all over, and that the strange tingling in his chest had given way to a burning sensation.

Oh well. At least he'd get to miss school tomorrow for sure, if it even was a school day. He couldn't be certain anymore.

Still, he continued trekking on, even when he had to duck twice onto side streets to sit against a wall for a few minutes, recover his breath and his strength. He stayed determined.

Just over half an hour later, he reached the house, and it had never seemed more welcome. Sans reached into the pocket of his sweat pants, fumbling with his key. Once he finally managed to get the door open, he stumbled inside and up to his room.

The lights were out, and the room was silent save for Papyrus' gentle, rhythmic breathing. A quick check proved him to be fast asleep. Good. That was good. Sans sagged against the crib as he reached inside to stroke his brother's skull a moment. The baby didn't even twitch. Sans smiled a little, then fell back onto his own bed.

He was tired. He wanted to have a nap. Just a little one.

Without bothering to shed the clothes he was wearing, Sans pulled his blankets over himself and tried to go to sleep. But the burning sensation in his chest was becoming hotter still, and at a certain point, Sans realised it didn't actually hurt per se. It was just a little… overwhelming. Distracting. And it was definitely keeping him up.

He opened his eyes and stroked his sternum, expecting the strange sensation to spread to his fingers, like the slight burning you felt when you brought your hand too near a candle flame, but he felt nothing. Curious now, he sat up a little in bed and poked at his soul experimentally. Still nothing.

Another poke, then suddenly, the feeling in his chest swelled, and he felt warm and empowered all at once. He felt strong.

His fingers twitched, and then, a tiny bone materialised, emitting a faint, muted glow. Sans' eyes widened, and he stared. The bone hovered in the air, just a few inches in front of him.

Magic.

He was doing magic.

He turned his hand this way and that, and the bone followed his commands as he guided it up and down, left and right. His fist closed, and the bone vanished.

"Whoa," he whispered to himself. And he tried again. This time, he drew energy from the strange new feeling in his chest without even having to think about it. It just felt right, natural somehow, an extension of his body.

Another bone materialised, this one a little larger than the first. He amused himself by steering it this way and that, even making it bob up and down rhythmically. And all of a sudden he didn't even feel tired, just excited, because he was doing magic, finally he was doing magic, and it was easy. At school, they said most monsters' magic didn't kick until the age of ten, and even if it arrived early, monster children had very little control over their abilities. The big kids at school all had special magic classes in the gym, which explained why the walls, floor, and ceiling were always covered in scorch marks. Sans used to sit on the playground at recess and watch as the big kids showed off the magic attacks they'd been mastering, when the teachers weren't around, longing to be able to do the same.

And now here he was, using, controlling his magic, three whole years before any of the kids in his class would even begin to learn.

He grinned to himself, a delighted giggle escaping him. He glanced over at Papyrus, but his brother was still fast asleep. Drawing more power from the feeling in his soul that he now knew must be the magical energy all big monsters gave off, Sans found himself summoning two, then three, then an entire collection of bones, floating before him, soldiers waiting for his command.

And command them he did, realising there were more patterns he could make. Irregular patterns, summoning more and more bones at will. Swallowing down the urge to shout for joy, Sans concentrated, then tried to do what he'd seen Gaster do. He gathered the bones a little closer together, then he thrust them out and away from him, in the direction of the door.

Crack. BOOM.

A surge of energy sent Sans flying back into his headboard, and he winced as his skull thumped against it. When he opened his eyes, he saw that the bones had embedded themselves into the door. They were fading now, but they'd damaged the wood, splintering cracks spiderwebbing from a small, smouldering hole.

In the same moment, Papyrus woke up and began to bawl at the top of his nonexistent lungs. Sans hissed under his breath, moving to climb out of bed and comfort him.

Then, from down the hall, rapid footsteps. They sounded angry.

Sans froze and stared, breathing hard.

The door whipped open, or what was left of it, and Gaster stopped and stood in its threshold.

Gaster stared too – at the demolished door, at the last of the bones that were fading, at Sans sitting rigid on his bed. Their eyes met.

Sans found that he was drawing himself inward, pressing himself against his headboard and holding his teddy bear tightly to his chest. He didn't dare let his gaze falter.

At some point Papyrus had stopped screaming.

A pause that might have lasted anywhere between ten seconds and ten minutes, and the whole time Sans continued staring, both fearfully and defiantly. And then Gaster turned on his heel and left, leaving the door open behind him.

Once he was out of sight, Sans' shoulders sagged, his bear falling out of his arms and onto his lap. Sans held up his teddy bear by one ear, studying it. Stupid bear.

Teddy bears were for baby bones. Stupid crybaby baby bones, not big kids who could use magic, who were strong.

He hated that bear.

In a fit of frustration that was novel to him, he summoned another bone, not even realising he was doing it, this one longer and thinner than the ones before it. He sent the bone flying forward. It embedded itself into the wall, piercing the teddy bear through its chest.

Pinned to the bone skewer, the teddy bear hung there limply, stuffing poking out of its wound. Eventually, the bone dissolved, and without anything to hold it up, the teddy bear fell to the floor.

Stupid, stupid pathetic bear.

Gaster didn't come running this time, and Sans let his hand fall to his side, dejected. He was really tired.

Eventually, Papyrus' thin whimpers gave way to rhythmic breathing. Once he was certain his brother wasn't going to hear him, Sans curled into a ball, hugging himself tightly, and cried himself to sleep.