The puzzles they came across were... significantly harder than the ones in the Ruins. Or at least, some of them were; Sans had the feeling he could pick out which puzzles were authored by Frisk, just based on the lower difficulty.
"IS THIS... JUST A CROSSWORD PUZZLE?" Papyrus asked, frowning faintly at the paper he held. "NO MATTER!" He pulled out a pencil and decisively wrote a 'Z' in every box. At the top, he scrawled, 'SNORE!' before placing the paper back on the ground.
Despite Papyrus' perpetually loud volume, they had yet to run across Chara. They had encountered several dogs, all of which Papyrus had been eager to pet. At one point, Sans had heard the distant clanking of Chara's armor, but Frisk had shown up and directed the brothers to hide behind a pair of large doghouses while they persuaded their sibling that their patrolling efforts would be better spent elsewhere.
"They've noticed that several puzzles have been solved," Frisk told the brothers afterward. "I tried to convince them that it was probably just Snowdrake looking for a captive audience, but I don't think they bought it. You'd best hurry."
After the crossword puzzle, they came across a hunk of cheese, frozen to a table. Squeaks came from a hole in the nearby wall. Knowing that the mouse might one day find a way to heat up the cheese... it filled Sans with determination.
The next area held a puzzle involving switches and Xs and Os that Sans couldn't make heads or tails of. Papyrus seemed to be slowly making headway, though, so Sans leaned against a tree and watched his brother work.
Idly he wondered: if this whole place was underground, how was it snowing right now? Were there somehow clouds down here? Was it just magic? He felt vaguely annoyed with the idea that magic was the explanation for everything down here. Of course, he had already seen magic with his own eyes - all the monsters seemed to wield it with ease in battle. And based off of the cleanliness of the stove top back in Toriel's house, she probably used her fire magic to cook as well as fight.
Still, personal magic was one thing. There were legends of human sorcerers as well - Sans had read of them eagerly, before... But that didn't explain the strange weather, or even the tree he was currently leaning against. Trees needed light to grow... but then, there was a muted light down here, wasn't there? Where did it come from? He squinted upwards, but the sky above was dark, empty of sun or moon or stars.
He found himself sliding down to sit on the ground. The snow was cold, and he huddled into his hoodie, breathing on his hands to try and warm them up. Every so often, Papyrus let out exclamations of frustration or victory. The victorious shouts seemed to be getting more frequent, so Sans didn't feel too bad about not helping out his brother on this one. They'd probably be moving on soon, on to whatever puzzle or challenge awaited them next. He could close his eyes for the moment, though.
Just for a moment...
"But how does it all work?" A frustrated voice.
A softer, voice, uncertain: "I... I don't know. Magic?"
A scowl. A pause. Finally: "Then how does the magic work?"
"SANS!"
He jerked awake, heart thudding. In front of him was his brother's concerned face.
"what? oh, hey... you solved the puzzle. nice work, bro."
Papyrus nodded distractedly. "I SHOULD HAVE KNOWN YOU WOULD NEED SOME TIME TO REST! PERHAPS... A PIGGYBACK RIDE, TO SAVE YOUR ENERGY?"
Sans looked down. "that's, uh, a nice thought. but i think that nap was enough." It did sound nice, but he was honestly kind of embarrassed at falling asleep instead of helping Papyrus with the puzzle. He should be trying to help them get out of this mess instead of taking naps like he was still a little kid.
What had that dream even been about, anyways?
"ARE YOU SURE? THE GREAT PAPYRUS IS ALWAYS READY TO SERVE AS YOUR CHARIOT, BROTHER!"
Sans laughed. Maybe it would be okay... He looked up - whether to accept his brother's offer or laugh it off, he wasn't sure - only to see a figure in dark steel standing by the solved puzzle. His heart dropped into his stomach, and he inwardly cursed himself for forgetting that this place wasn't safe.
Apparently Chara could move quietly, when they wanted to.
"Two humans?" they said. "It must be my lucky day."
Slowly, Papyrus turned around, shielding Sans as best he could. "YES!" he shouted, exuberantly, and only a touch nervously. "YOU ARE INDEED LUCKY TO MEET MY BROTHER AND I, FOR WE ARE THE BEST HUMANS WE KNOW!"
Sans peered around his brother. This time, the skeleton was wearing a helmet, but it was definitely Chara. Their armor proudly displayed an emblem: a bone crossed with a knife. He shivered a little, seeing it.
Realizing he was still slumped against the tree, he stood up. Chara seemed less than impressed with his brother's bravado. He almost wondered if Frisk would show up to help... but Frisk had advised them to avoid Chara, to not be caught by them. They probably wouldn't be able to help, now that he and Papyrus were actually facing their sibling.
"Today is a fateful day," Chara said. "You two are going to help me fulfill all of my hopes and dreams."
Papyrus and Sans' souls floated out from their bodies, a motion that was already becoming familiar to them both. The sight of their dual blue souls would almost be comforting, if it didn't signify the start of a battle.
"ARE YOU THE AUTHOR OF THIS PUZZLE?" Papyrus asked. "BECAUSE IT IS TRULY MAGNIFICENT!"
"Well, it trapped you here. So I guess I agree." And with that, they smiled... and threw a flurry of bones at the brothers' souls.
Sans tried his best to dodge the bone onslaught, but his soul was clipped by a few of the bones. Papyrus was even worse off - he was better at talking to monsters rather than dodging their attacks.
"AHAH... TRULY, YOU ARE A FORMIDABLE FOE! I MUST SAY -"
Chara cut him off, hurling another wave of bones at their souls. Sans fell into the rhythm of dodging, but Papyrus yelped, caught off guard, and was battered by bones as a result.
When the bone attack was over, Papyrus opened his mouth to chastise Chara for interrupting him. Sans shoved a Nice Cream bar into his hands instead. "you're low on health," he said, "and i don't think they want to listen anyways."
Papyrus frowned, but ate the Nice Cream. The wrapper offered him an illustration of a hug.
Chara wasted no time in attacking, this time swiping at the brothers' souls with a pair of large bones.
"YOU KNOW, INTERRUPTING PEOPLE IS RUDE! AND SO IS ATTACKING THEM! DO NOT FEAR, HOWEVER! I WILL FIND IT IN MY HEART TO FORGIVE YOU!"
Sans inwardly groaned. Papyrus should really be taking his turns to heal, not try and forgive their murderous opponent.
Papyrus' offer of forgiveness elicited no reaction - other than another bone attack, of course.
"AH, BUT I AM AFRAID THAT FORGIVENESS SHALL HAVE TO WAIT UNTIL AFTER WE STOP FIGHTING! BY THE WAY... HAS ANYONE EVER TOLD YOU THAT YOUR ARMOR IS REALLY COOL?"
This, of all things, seemed to take the skeleton aback. "Only Frisk... Thanks?" they said, before throwing yet more bones.
"YOU'RE WELCOME!" Papyrus shouted cheerfully. He seemed to have completely disregarded the idea of healing.
'If he takes any more hits, I'm going to force-feed him the butterscotch pie,' Sans swore silently.
Papyrus continued, "NOW, BEFORE THIS BATTLE, YOU SAID WE WOULD HELP YOU WITH YOUR HOPES AND DREAMS..."
Another flurry of bones, but the pattern was growing familiar; even Papyrus managed not to get hit, and Sans dodged them with ease.
"...AND I KNOW JUST HOW WE CAN MAKE THAT HAPPEN! YOU SEE, I KNOW IT IS EVERYONE'S DREAM TO HAVE FRIENDS AS COOL AS MY BROTHER AND I!"
Chara attacked again, but their bones seemed to be moving... slower? Sans couldn't believe it. Was his brother really getting through to them?
"WELL, WE CAN MAKE THAT DREAM OF YOURS COME TRUE! YOU SEEM LIKE A GREAT PERSON, AND MY BROTHER AND I WOULD LOVE TO BE YOUR FRIENDS! ISN'T THAT RIGHT, SANS?"
Sans forced a smile. Making friends with a would-be-murderer wasn't exactly his idea of a good time, but... well, it would definitely be easier than fighting them. "yeah, bro. friendship to the max."
A few bones flew towards them, but both brothers could easily move their souls out of the way. Sans felt hope stirring in him.
"WHAT DO YOU SAY?"
The skeleton lifted up the faceplate of their helmet, and looked at the brothers. A small smile crept onto their face. "Sure," they said. "Let's be friends."
Sans sighed in relief, while Papyrus grinned ear-to-ear. "GREAT!" he shouted. "I AM VERY GLAD -"
Then one of Chara's eyesockets flashed red, and twin knives struck twin souls.
The worst part wasn't even that Sans could feel his soul about to shatter, or that he could feel the knife like it had pierced his actual heart, or that Chara was striding forward to collect his soul, a cruel smile on their face.
The worst part was the stricken, betrayed look on his brother's face, before everything faded away.
...
..
.
Where he expected to hear nothing, he heard a deep voice.
"Our fate rests upon you... My son, please... stay determined..."
Sans felt a fire ignite within him, a burning sensation in his soul. Their story could not, would not end that way. He would not let his brother die to that monstrous skeleton.
He refused.
Get.
Knifed on.