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Why Children Climb Mountains

(you have a home right here)

Bonus Chapter

Sans

Oliver ran as fast as his legs could carry him through the dense forest bordering the town. He didn't stop, even though his legs were starting to cramp up and his chest was burning. The overuse of his magic sent spasms of agony through his body. He almost lost his footing a few times as shadowed roots and bushes obstructed his path.

He'd really done it this time. Of all the stunts he'd pulled in the past, this was the one that assured he no longer had a home to return to. He should have felt sad about that, and maybe if his family were anything close to the average, loving kind he would've, but instead, all he felt was relief. He was getting out of here; out of this town where fear and prejudice ruled people's hearts and centuries of tradition and control kept anything from changing. Oliver didn't need any of them. He was powerful. His family knew they couldn't control him. Their magic was only a shadow of what it had been back when they'd reigned above all other magician families in the West.

Above the fleeing boy, Mt. Ebott loomed, magnificent and foreboding. It was the one place where his family wouldn't look for him. They dared not trespass there for fear of the evil long sealed within; the monsters they themselves had trapped there nearly a millennium ago using the blood of their own clan. Oliver felt sweet vindication at using their own superstitions against them.

The hike up the mountain was slow, but Oliver persevered. He was driven not by determination but necessity and a sense of self-preservation. If the police caught him before he made it to the top, he'd be sent back to those doctors. With a generous lump of money from his parents, they would use both tools and medication to fiddle with his brain until his spirit broke and he became the perfect, obedient child his family always wanted. Oliver knew it was fear that drove his parents' actions. They loathed not being in control and they couldn't stand that Oliver was born with so much magical talent while both of them only barely had the gift.

At the top of the mountain, Oliver found what he was looking for. There, like a crater straight to hell, was the entrance to the monsters' realm. It was an enormous gaping maw that looked like it could swallow him up at any moment. That was the plan, though. Taking one last look back toward the world he would be leaving behind, Oliver Winterlance offered a two fingered salute and took a running leap into the darkness below.

oO0Oo

The first time Gaster took him to Asgore's palace, Oliver was somewhat annoyed. Why did he have to leave his work to follow his mentor to a meeting where he would just stand there silently the whole time? There was no point.

"Come, Sans," the tall royal scientist said gently, an air of amusement about him. He could tell Oliver was sulking and he found it charming, as he often did Oliver's quirks. Weirdo. "You may be surprised by what you can discover when you take the time to observe and interact with the world at large. Perhaps you will even find the thing you lack."

Oliver looked up at his mentor flatly. "Am I lacking something?"

Gaster chuckled. "Oh, very much so," he answered, folding his long fingers together the way he always did when contemplating the results of a test. "Consider my request part of an experiment. You needn't concern yourself with the details, simply do as I ask and I predict we will arrive at a result that is mutually beneficial."

Oliver sighed and stood from the machine he'd been tinkering with. He grabbed a cloth and wiped down his hands. Gaster seemed pleased by his obedience. "Are you prepared?" he asked, holding out a hand to the young human.

"Just a sec," Oliver answered, turning from the dark robed scientist to fumble with something high on a shelf. A second later, he'd retrieved a nondescript looking box large enough to hold a basketball. He carefully pulled the top off and slipped his hands inside. From out of the box he lifted a large white skull and a pair of gloves designed to resemble a skeleton's hands. The skull's eye sockets were dark and the mouth wore a large, toothy grin. Gaster looked on with interest.

"What's this?" he asked, inspecting the skull inquisitively. He brought his own skeletal fingers to his mouth as his eyes roamed over the dips and curves of the synthetic cranium.

Oliver shrugged. "I figured it would only cause problems if I went out looking like a human so I made this mask to fit in better." He looked to his mentor for his professional opinion. "What do you think? I modeled it after my favorite smiley old geezer."

Gaster touched the skull's crown delicately. "It's exquisite," he praised, tracing a finger from top of the cranium down to the arch of the zygomatic bone. "A little glamor and I imagine you will fit in quite impeccably." Looking back at Oliver, he tilted his head questioningly. "Do you fear you won't be accepted as you are?"

Oliver knew he wasn't judging him; he was simply curious. Gaster was always analyzing and examining. The world was endlessly fascinating to him; like a newborn with the brain of a supercomputer. He smiled slightly at his mentor's question. "I already left my humanity behind. Isn't it just easier not to deal with the questions? After all, I'm Sans now. For all intents and purposes, Oliver is dead."

oO0Oo

"Sans, I have a surprise for you."

Sans perked up and set aside the joke book he'd been perusing out of boredom. "What's up Gastman?"

Gaster gestured for his young protégé to follow. "Come. Walk with me to the fifth lab. Your surprise is waiting there."

Interested, Sans hopped off his chair and fell into step with the scientist. Gaster's strides were long and unhurried but Sans had to powerwalk to keep up. Despite all the years that had passed since he fled his town, Sans had only physically aged about a year and he was still quite small, not yet having hit his growth spurt.

The two researchers reached the lab a few minutes later and Sans looked around the place curiously as he entered. Nothing seemed different until he caught sight of a large tank off in the corner in an area that was slightly less cluttered than the rest of the lab. In it, a small form floated in yellow liquid.

Sans stepped closer and peered through the glass. Through the cloudy liquid, he was able to make out the figure of a monster. It was a skeleton type, tiny like a human toddler.

"Meet Papyrus," Gaster said, coming to stand beside him. "He's a product of my magic and the Determination I harvested from you over the past few years. I suppose that in essence he's not dissimilar to the concept of a brother."

Sans turned away from the small skeleton to look at Gaster with amazement. "A monster made of Determination? How is that possible?"

Gaster's smile widened. "Oh, I do wonder. We will have to see if he is able to maintain his form after he's discharged from his tank." He raised one slender, tapered finger and pointed to the release button. "Would you like to do the honors?"

Sans gulped and looked back at the small form floating in the liquid. If Gaster's experiment was a success, he would have a new monster sibling. But if it failed, Sans would watch this small life fizzle out right before his eyes. It was a difficult decision but Sans summoned up every ounce of his meager determination and pressed the button.

The capsule made a beeping noise and the fluid drained from the tank revealing Papyrus in all his tiny glory. The glass front of the tank swung open and Sans held his breath as he waited for whatever would come next. A few heartbeats later, the small skeleton twitched and opened his eye sockets. He looked right at Sans with an expression full of wonder.

Sans let out the breath he'd been holding and reached out to take Papyrus' hand. "hey, little bro," he greeted, adopting a goofy voice in order to make himself seem more friendly. "welcome to the world. it's big and scary and full of struggles but it's home."

Papyrus blinked up at him and then tightened his little phalanges around Sans' gloved hand and giggled happily.

Sans felt his heart fill with affection for Papyrus' small self and he took the little skeleton into his arms. He looked up at Gaster and his eyes shone with joy even through his skull mask. "i guess our family just grew."

oO0Oo

The day that Frisk came, Sans felt his soul come alive for the first time in almost longer than he could remember. Over and over and over and over and over he'd endured as the world was reset again and again and again. He'd almost gone mad with all the resets—almost stopped believing they would ever end. But that day, the woman on the other side of the door to the ruins said something different than usual.

"If a human ever comes through this door... could you please, please promise something? Watch over them and protect them, will you not?"

A new face appeared in the underground that day. A human child Sans had never seen before. He judged them to be about the same age he himself had been when he first came to the underground. The child was small and quiet and obedient; a tiny thing with a sweet face and the will to please. Perhaps they were just another child come to their death, but maybe, just maybe, they were a sign that the countless resets were finally finished. For the first time in ages, Sans felt determination stir in his soul.

Papyrus became fast friends with the child. He had always wanted to meet a human and this one did not disappoint. Papyrus was an innocent soul full of curiosity and dreams and it made Sans' heart glad to see him having so much fun. Sans continued to observe the child with growing hope as they made their way through the underground without taking a single life. They were an extraordinary human, full of compassion and kindness the likes of which Sans had never met either in the underground or on the surface. Even Sans, cynical and mistrustful of humans as he was, found himself charmed by young Frisk.

He followed them through their journey, keeping an eye on their progress and interacting with them when it suited him. The more time he spent with Frisk, the more attached Sans became to them. He'd thought he was done with humans and their world, but this child, this kid who had climbed Mt. Ebott and tumbled into the underground with only goodness in their heart intrigued him and enticed him. He wanted them to succeed. He wanted to believe that humans were capable of love; because maybe if this child was, then he was too.

When it finally came time for him meet them for the last time in the Judgement Hall, Sans was sure: this was the human who would do what he never could. They would break the barrier and set monsterkind free. They had the Determination to make anything possible. When Sans saw them off to meet the king, he wore a true smile beneath his mask.

The next thing he knew, though, he was waking up in his bed, right back where he'd started.

Sans gripped his mask and breathed in and out, in and out, in and out, and screamed.

oO0Oo

Over and over and over.

Over and over and over and over.

Sans felt his mind slipping. He was going to crack soon. He swore he was. This—this monster child was going to make him lose the plot. This wasn't Frisk. This demon wasn't the sweet, kind child he'd known before the reset. This one was a true monster. They came at him again and again with a heart full of violence. They felt no remorse. They delighted in what they'd done. They were the hatred and animosity of his parents and all the people of his hometown all contained in one neat package. Thirty years of hiding away, never seeing the sun or showing his face, and he still couldn't get away.

When the deathblow finally came, it was almost a relief. Sans had already known he didn't have the determination needed to save everyone in the underground, but he'd thought maybe he could keep the demon from escaping to the surface, at least. Now that Sans knew good humans like Frisk existed, he wanted to do what he could to keep them safe. But in the end, the demon's Determination was mightier than Sans' magic.

If only he had that kind of Determination, he thought as darkness took him. If only he knew how to keep trying.

oO0Oo

It was difficult keeping up the pretense of being a monster on the surface. The small bits of magic he used every day, such as glamoring his mask and using shortcuts and keeping himself warm in the cold winter now taxed him greatly. Humans weren't built to use magic constantly and Sans had learned this firsthand in the eleven months following the monsters' departure from the underground. For the sakes of his brother and friends, though, he persevered.

Pretending only continued to get harder, however. As the months passed, Sans noticed that he'd begun to age at a normal rate once again. He was getting taller quickly and soon people would start to notice. What's more, he was spending more and more time sleeping as his body tried its best to recover from his overclocked magic consumption. He was forced to hide out in his workshop to eat and give his body a break. Sometimes he wondered why the only determination he could muster was the determination to keep hiding. He had made his choice long ago, though. He'd left Oliver behind to become a monster and he wouldn't look back. His friends needed him and there was no home left for Oliver anyway.

In truth, Sans hadn't thought about his human life in a very long time. He liked his life as it was now. Sans had everything Oliver had ever wanted; good friends, a loving family, and hope for the future. He was ecstatic to wake up in the morning knowing that every day was a gift and he had the freedom to do anything he wanted; to be anything he wanted. And in all this, he found himself inexplicably drawn to Frisk. Sans had never connected well with his own kind, but Frisk was different. Frisk was so kind and lovely and charismatic. The more time Sans spent with them, the more his feelings took root. He began looking for excuses to spend time with them. He really believed that he had found the true timeline at last. After all, how could this be wrong when it felt so right?

But then, his father had gone and stuck his nose where it didn't belong. It rankled Sans how the old geezer pretended to be concerned about the missing children when Sans knew he was really just acting out on his hatred of monsterkind. If he had really cared about the children, he would've cared about his own son. But he didn't. He was driven by bitterness, not love, and Sans almost wanted to reveal himself just to call him out in front of everyone but he knew nothing good would come of it. Sans had a backing and was influential but Oliver was just a lonely psychopath who had been declared dead thirty years ago. Sans had power. Oliver had nothing. If he was going to affect anything, it was going to be as Sans.

But what could Sans do, really? On the surface he had low magic and even lower determination. Even underground, he couldn't stop one child from destroying everything he loved. All Sans had ever been able to do was watch his friends die. He would help out where he could, but ultimately it would be up to the humans and the boss monsters to determine how this affair turned out. He was already at his limit just maintaining his life as Sans.

But then Frisk showed up, crying, in his workshop. Sans had thought his hands were tied, but when he saw Frisk sitting there lost and alone and in tears he saw himself from all those years ago. He saw young Oliver hiding away, alone and helpless, and suddenly he was filled with determination. He wanted to protect Frisk. More than anything he wanted to keep them safe and happy because they were good and pure and full of light and fuck anybody who thought they could do to Frisk what they'd done to him. Not on his watch.

Sans had never planned to go back to being Oliver. He'd said goodbye and good riddance and washed his hands of his past life and he was happier now than he'd ever been as a human. He certainly never would have predicted that Oliver could be the answer to saving all of monsterkind. In the end, the price of peace would amount to the sacrifice of a single monster.

Honestly, Sans hadn't known if he was going to survive his stunt in the council chamber or not. He knew his limits and he knew that he was going to have to expend tremendous amounts of magic if he wanted to avoid being captured and facing capital punishment, but it was either get arrested and be killed or try to escape and probably kill himself. He banked on the latter. After all, he'd made a promise. He'd given Frisk his word that everything would be okay and he was determined—by god, he was DETERMINED—to keep it.

oO0Oo

Sans—no, Oliver held Frisk tightly against him. He smiled as he relished in the feeling of their hair pressed to his cheek—his flesh and blood cheek, not his mask. It felt like rebirth, reemerging from the underground the way he'd first entered it, a human too small for the world but secure in the knowledge that he was on his way to a better place.

Frisk was crying. Oliver thought about how many tears had been shed for him in the month following his disappearance and he squeezed Frisk's small frame tighter in apology and in reassurance that everything would be okay now, just as he'd promised, and also in gratitude to them for keeping their end of their promise. Frisk squeezed back and buried their face further into his neck. They held him like they feared he would vanish in an instant if they so much as loosened their grip.

But Oliver wasn't going anywhere. He'd fought with every ounce of determination he had to come back, and for better or worse, he was here to stay.

It had felt like his soul was being ripped into pieces when he'd faced off against the ring human soldiers in city hall. The human body was a finite container and Sans had tapped himself well and truly out with all the magic he'd used to construct such an enormous and complex illusion. In the end it had been determination alone that had given him the strength he needed to teleport out of chaotic council chamber and to the entrance of the underground. There, he'd lain for seven hours, bloodied from two gunshot wounds to the thigh and barely hanging on as his soul tried to shatter. Both his body and soul had screamed at him that he was finished; that he'd already passed his breaking point; but he thought of his brother and his friends and his promise to Frisk and he grasped at the life that still awaited him and hung on for everything he was worth.

It had taken four weeks for him to heal. In the underground, he had access to all the magic he needed and his reserves were able to refill quickly. After that, he'd just needed to wait for his body to mend. With the help of monster food, he'd made a full recovery in a fraction of the time it would've taken him on the surface. With each passing day he'd become stronger until finally he was able to make his way to Hotland and what little remained of his old home; the secret set of labs hidden away beneath Alphys' home, deeper even than the True Lab. There, he had removed his mask for the final time and set it delicately on a dusty shelf beside his old joke book and a box containing Papyrus' first attacks. It was in that lab full of memories that Oliver had at last said goodbye to Sans.

When Frisk's tears finally dried up, Oliver pulled back gently. "hey," he said, using a hand to delicately nudge their chin upward to look at him. He rewarded their compliance with a sunny smile. This was it; following this moment was the start of a new adventure for Oliver Winterlance. He was apprehensive, but far greater than that, he was filled with determination. "let's go home."

oO0Oo

Aaaaaaand we're done! Thank you so, so much to all the people who followed, favorited, and commented on this story. You all are wonderful and I hope you enjoyed reading this story as much as I did writing it. As usual, special thanks go to coincidencless, Tai-ke-ai, PanicAtTheBombShelter, BlackJap, Liliana Dragonshard, The Rude Girl, The Jabberwock of OZ, and SneaselXRiolu for their lovely comments on chapter seven. You guys are the raddest.

I'm sorry this chapter was so much later than all the others. I'm on vacation in Hawaii right now with my family so I've been really busy every day. It took ages to find a moment to finish this chapter.

To be honest, this whole story came about because of all the Undertale fanfiction I've read—which is admittedly probably not as much as all of you—I'd never seen anyone tackle the Sans-is-actually-a-human theory. Of course, Sans is awesome no matter what race/species he is. I just wanted to provide a somewhat convincing explanation as to how human!Sans could be a thing without changing the canon.

This story is now officially complete. However, I am still considering writing other pieces that fit into this universe. Probably some sequel-ish oneshots. I dunno. Or maybe I'll write an entirely different Undertale story. Who can say? In any case, I've enjoyed writing Why Children Climb Mountains immensely and I couldn't be happier to have such awesome readers.

Ciao for now!

Allison