It started off as a normal day. Nothing should have happened that was out of the ordinary. But this was the Underground – a place wherein the known laws of physics, of time and space, fluctuated as they saw fit without the slightest warning or regard for contradiction. And so it started off as a normal day, but it certainly wasn't going to end that way.

Sans spent the day lazing around Grillby's bar. It was the ideal place to hide from Papyrus and his jobs despite how he was aware it was where he spent all of his time. Still, for some reason, the place seemed to ward him off – fortunately for the smaller skeleton on his laziest of days. He was thus spending a nice time in the company of friends, cracking jokes and munching on excellent food. Hours flew by in what felt like mere minutes what with all the fun they were having. Before anyone knew it, Grillby was reminding everyone of the time and the usual crowd of monsters steadily began to disperse. First, Dogamy and Dogressa needed to return home to freshen up for their date night whereas as Ugly Fish had plans to set a lure by the river in order to seduce a fish or anyone curious enough to retrieve his message. In half an hour or so, the remaining dog monsters would also leave to their own devices and, after an additional hour, everyone but Sans would be gone.

But this wasn't a normal day.

"Shouldn't you be getting home?" Grillby asked Sans. "I can't imagine Papyrus will be too pleased with you today."

"he'll be furious." Sans agreed with a laid back chuckle.

"Best to head back now and face the thunder." Grillby recommended.

"this is why you're the sensible one." Sans grinned as he hopped off the stool. "but you're right. i might even be able to control the damage."

"I'll walk you to the door." Grillby offered.

Sans waited for the bartender to circle around the counter and then walked with him to the door. Grillby, ever the gentleman, held the door open for him. Sans responded with a curtsy as a joke – one that effectively got a laugh out of the other. They stepped out of the bar and into the snowy street. The monsters of Snowdin were heading home while the children continued to play their games. But soon, it would be time for dinner and the streets would, as a result, go empty.

"It's chilly today." Grillby remarked.

"yeah, your flames are receding." Sans noted.

Grillby reached at the top of his head, feeling the diminishing flames. "Hun. You're right." He hummed in relative surprise, "Best I not stay out for too long."

"well i won't keep you." Sans assured, stuffing his hands into his pockets. "i've got a lecture to attend."

"I'll see you tomorrow then." Grillby smiled and gave a small wave.

"maybe tonight if i'm not grounded." Sans snickered.

"I've never known Papyrus to go easy on you when—"

But Grillby never finished his sentence. He was unexpectedly interrupted by the deafening sound of an explosion. The ruckus had almost startled Sans's soul out of his body. He agitatedly turned around, facing the direction from which it had come only to see frightened monsters sprinting away and children running into their homes. In the distance, he could see smoke rising from the treetops. It almost looked like it was coming from his house, but Sans dismissed the thought. There was no way. It would be impossible—

"Sans!" A monster shouted, running towards him with a concerned expression on its face. "The explosion—it came from your house!"

"Shit." Grillby muttered in shocked horror. A string of more colourful words instead came to Sans's very worried mind.

"I think Papyrus was inside." It added.

Terror immediately took over him. Never had a sentence brought about so much dread and fear. So much so, Sans found himself paralysed. His thoughts rushed and he wondered if his brother had died. The sound had been so loud and the smoke coming from his house was so dark. Though Papyrus was privy to a lot of hp, the presumed impact of the blast might have been enough to dust him. The last thing he wanted was to return home and find a pile of dust waiting for him amidst the ruin of his – their home.

"Sans!" Grillby snapped, bringing him out of his thoughts. "What are you waiting for!? Go! I'll try to contact Undyne."

"r…right." Sans nodded sheepishly. He shut his eyes tightly and shook his head, clearing the obstructing thoughts from his mind. "right!"

And without wasting an additional moment, he ran home. The snow slowed him down, but the adrenaline almost made up for it. His legs pumped as fast as they could, carrying him to his home in near record time. Despite what the explosion may have suggested, Sans wasn't greeted with a pile of rubble, but rather an intact establishment – no different from how he had left it that morning. However, black smoke rose and it took him little time to realise it was coming from his secret lab.

The smaller skeleton circled around the house and easily busted down the door he usually kept locked and shut. If Papyrus had caused the explosion, how had he gotten in? He shouldn't even have been aware of the compartment in the first place. And yet, when the smoke cleared up, Sans found his brother wielding a fire extinguisher and putting out the last of the fire. He coughed violently and wiped the sweat from his brow then turning to find Sans standing in the doorway.

"Sans!" Papyrus yelped and suddenly looked very nervous. "W-what are you doing here?"

"what happened?" Sans demanded taking a step forward. Papyrus took an anxious step back. "are you hurt?"

"I-I'm fine." Papyrus laughed tensely, "Just, you know, a small explosion. Nothing to worry about."

"nothing to worry about?!" Sans snapped, losing his composure. His hands were trembling. "there was a thick column of smoke coming from the house—i heard the explosion all the way from grillby's! a-and what are you even doing here? how do you know about this place?"

"Don't be mad!" Papyrus pleaded, pressing his hands together as he cowered. It made Sans feel a little bad for his outburst. But only a little. "I was mad that you played hooky and decided I would clean your room – I know how much you hate it when I do that. I was looking through your sock drawer when a key suddenly appeared in my pocket. It took me an hour to find this place. Speaking of," Papyrus's tone suddenly became reproachful, "how come I didn't know about this? Why were you—"

"what exploded, papyrus?" Sans demanded, ignoring the question. He would answer it and the others that would undoubtedly follow later, but there were more pressing matters at hand.

Papyrus suddenly looked very nervous again. "N…nothing?"

But just as he lied, the bulk of the smoke behind him cleared up and revealed the machine Sans had been keeping beneath a tarp for many years. The contraption was round and hummed lowly with a glass door that pulsed a bright blue light. Sans all but gasped at the sight of it. He knew very little about the machine he kept hidden. A feeling in his soul told him that it belonged to him, but nothing more. It stemmed from a period in his life that he couldn't quite recall. He had tried fixing it in his spare time a decade ago, but later gave up due to lack of any kind of progress.

"what did you…do?" Sans breathed in a mixture of awe and fear. He didn't know what the machine was meant for. Not even the blueprints he kept locked away in his desk could give even the slightest hint.

"I fixed it, I think." Papyrus admitted, glancing at his feet awkwardly. "Don't be mad."

"just get away from it." Sans sighed. "you're too close, it's making me anxious." Papyrus obliged, moving to his brother's side. The latter wasted no time to grab him and inspect him to make sure he was truly alright. "you're sure you're not hurting anywhere?"

"I'm fine, Sans." Papyrus insisted, "I was just a bit startled."

Sans looked him over for a moment longer before eventually nodding. "so what did you do?"

"I poked around." Papyrus replied with a slight wince, expecting a scolding the more he elaborated. "It looked like a puzzle so I solved it and then it blew up."

"a…puzzle?" Sans repeated. He didn't recall anything remotely resembling a puzzle. Then again, his brother had a unique way of looking at the world.

"Yes. It was actually quite fun." Papyrus smiled.

"you shouldn't have done that." Sans exhaled and apprehensively took a step towards the machine. "i don't know what this thing does. we need to shut it down. how did you turn it on?"

Papyrus looked at him with big clueless eyes before shrugging his ignorance. Sans sighed again and gulped thickly as he returned his gaze to the daunting machine. He was going to have to figure it out himself, something he wasn't keen on doing if it meant another explosion. With 1 hp, he wasn't particularly fond of taking risks. But this was important. There was no telling what the machine did and even the slightest possibility of it being nefarious meant it had to be shut down. It was for the good of the monsters. If he survived, he was definitely going to give Papyrus a stern talking to.

"stand by the door, papyrus." Sans ordered as he steadily got closer.

Papyrus did as he was told with little protest. He probably knew he would be in trouble for invading in Sans's privacy, but for also meddling with something he didn't understand. Now closer to the machine, Sans found himself holding his breath. It was resonating and the pulse rumbled through his bones in a very strange way. It almost seemed like it was beckoning him to move in a specific way. The gamble was whether to concede or not. Sans deduced it was wiser to use his brain over his instinct in the given situation. There was no control panel or wiring visible on the exterior of the machine which therefore left him with the only option of opening the door. He took in a deep breath and reached for the handle, stiffening when the pulsing and humming abruptly stopped.

Sans glanced back one more time at Papyrus who seemed as anxious as he felt before he opened the door. Suddenly, there was a blinding light and the deafening sound of something akin to thunder but worse – as though the fabric of time and space was ripping itself apart. He was hit by a powerful blast that swept him off his feet. Sans wondered if this was what it was like when monsters died. The world around him was no more. Papyrus was gone. His lab was gone. Everything was gone. He felt himself floating weightlessly in a white abyss – the afterlife, Sans supposed. He figured it would be a dull, empty place. But then he soon found himself falling. The whiteness faded into blackness and then colour. He felt like he was falling for ages until he suddenly hit the ground with a near bone-shattering force. Black spots invaded his vision and he felt himself slipping away.

The last thing Sans thought he saw before he died was the vague silhouette of Papyrus and a pair of red eyes.

When Sans came to, 'confused' wasn't the right word to describe how he felt but it was the only one that came to mind. His blurred vision eventually focused on a familiar grainy ceiling and just when he understood what he was looking at, he realised he was lying on a rather comfortable bed. His bed. Shortly after, he however noticed there was a less than comfortable shackle tied around his ankle. Sans pushed himself up with his forearms and glanced at his legs to find the left one had been tied to the bed. The shackle wasn't too tight, but it was heavy and it weighed down his already aching leg. In fact, his entire body felt sore.

The smaller skeleton allowed himself to fall back against the bed. He extended his arms and sighed deeply, regretting the action mere seconds later when his bones seized in protest. His entire body hurt. He vaguely remembered falling hard against the ground. Now that he thought about it, it was kind of incredible that his fall hadn't been enough to deplete him of his hp – though he wasn't complaining. He was alive somehow even if he had been sure he had died. Sans shut his eyes and considered what must have transpired instead. The machine probably exploded a second time and knocked him out of his lab. Papyrus probably picked him up and brought him into his room. Sans shifted, jingling the chain bound to his leg and the bed. If Papyrus had truly brought him back to his room, then why had he decided to tie him in place? What was the point?

And almost as though it were on cue, the door to his room suddenly clicked open. Sans pushed himself up again and was startled by who he found. It certainly looked like Papyrus…but it also didn't. The skeleton he was confronted with was probably an inch or two taller than his brother and possessed a wider build. He wore black armour decorated with a silver sigil and two badges that were partially covered by the crimson scarf he wore loosely around his neck. His cheekbones were sharp and defined and his teeth were menacingly shark-like. However, his most striking features were likely his red eyes and the scar that sliced through his right one.

"Oh good. You're awake." He said with feigned interest. Sans apprehensively watched the skeleton strut to a chair at the opposite side of the room before dragging it by his bedside. He then took a seat and looked at Sans expectantly. "Well?" He demanded, after an extended moment.

"who…are you?" Sans asked slowly.

Probably the most astonishing thing about the stranger, aside from the weird subtle similarities to Papyrus, was that he was a skeleton. As far as Sans was concerned, he and Papyrus were the only monsters of such a kind in the Underground. Where had this one been hiding all this time? And why? He moved slightly and his chain clanked once more, reminding him of his very vulnerable situation. If the other decided he wanted to kill him, there was little he could do to stop him. The shackle prevented him from teleporting away and so his life was literally out of his hands.

"No, that's the question you're supposed to be answering." The skeleton corrected with a hint of annoyance.

Sans didn't understand.

"i'm…sans." He said and tensed when the other skeleton didn't seem to like his answer. "who are you?"

"No, who are you?" The stranger instead repeated aggressively.

Sans didn't understand what kind of answer he wanted if not his name. "i'm sans…sans the skeleton…"

"Do I look stupid to you?" The skeleton hissed.

Sans leaned back uneasily. He didn't understand. Why was his answer unacceptable? "what do you want me to say?"

"The truth." He snapped, closing his hands into fists. It seemed he was currently running the risk of getting slugged probably in the face.

"i've been telling you the truth! what do you want me to say!?" Sans retorted in frustration. It was a risky move to blow up in such a fashion, but he didn't know what else to do. Not only that, but he too had questions of his own he wanted answered. "and why am i here? where's my brother?"

The skeleton seemed to calm his temper despite still being visibly irritated. He seemed particularly interested in the last question he had posed. "I didn't see anyone else when I found you." He replied, "You have a brother?"

Sans nodded slowly. He wasn't sure whether telling him was a good idea or not, but he didn't have many options at his disposal. "his name's papyrus." He supplied, "he—" but he interrupted himself when the other's face contorted in confusion. "…what?"

"Are you…" The skeleton started but seemed unsure on how to proceed. "Are you…something Alphys created? Are you some joke robot she sent to taunt me?"

"w-what? no!" Sans stammered and grimaced as well. "no! what the hell?"

How did this stranger know Alphys? The yellow dinosaur wasn't a very social creature and was easily intimidated. Sans found it hard to believe the two knew each other and that they were good enough friends for her to send him robots as a joke. But why would she make robots of him and send it to someone he didn't know? He was starting to develop a headache. Later, when he had the time, he would need to search the dictionary for a word that better defined the level of confusion he was experiencing.

"Then who the fuck are you!?" The skeleton snapped and lunged out of his chair, grabbing Sans by his sweater. "You're not a fucking robot and you're not Sans so who are you!?"

Sans gritted his teeth together and anxiously gripped the large hand that squeezed the fabric of his shirt and sweater so uncomfortably around his neck. He didn't know what to say. He wasn't lying and yet the other didn't seem to believe him. "i am sans!" He insisted, "i don't know what to tell you or how to prove it!"

"You're not Sans!" The skeleton shouted.

"why do you keep saying that!?" Sans barked. He was truly at his wit's end.

"Because I would recognise my own brother!" The skeleton growled.

The exclamation brought about of wave of tense silence that froze them both in place. Sans took a minute to process what the affirmation meant, thoroughly confused by it. He only had one brother and it was Papyrus. Was this skeleton suggesting he was his long lost youngest or oldest brother? How was this making any sense?

"what's your name?" Sans asked as he desperately tried to make sense of what was going on.

"Papyrus." The taller skeleton answered. And slowly, things began to click into place. "I'm first lieutenant of the Royal Guard, bound to the service of King Asgore and charged with the protection of the Snowdin region. Now who are you?"