Sans rocked back on his heel bones, staring down into the hole that Frisk had fallen into the Underground through with disdain, his trademark grin tense and uncomfortable. One of the first things he'd learned about the Surface was that there were no Resets here. No Save points, no timeline jumping, no do overs. He'd been filled with the most profound sense of relief upon this realization, feeling finally free of the constant fear of the Resets that had plagued him in the Underground. Which was why he was so disturbed now. If there was no more Save and Reset options, then why was there still an active anomaly in the timelines? He hardly needed to look at the reports to notice this one. It came with a queer twisting feeling in his soul. It made his bones feel hallow and kept him from sleep more often than not. He couldn't describe why exactly he felt so unnerved, only that he did.
That's why he'd volunteered to join the team of human scientists, and Alphys, that were planning an expedition to study the Underground, now that the barrier was destroyed and the way was open into and out of the mountain freely. It'd come as quite the shock to everyone, especially Papyrus, that the infamous lazybones would willingly volunteer to work. Sans had laughed, passing his decision off by saying that someone had to go and watch out for Frisk who, as monsterkind's human ambassador, was obligated to go as well. After that, it had taken a good three hours to convince him and Undyne that no, they didn't need to come as well. It took a very pointed blue-eyed glare to Undyne when Papyrus wasn't looking to finally get her to settle on the matter, too.
Frisk knew better, of course. They remembered the Resets, they felt that something was wrong. They knew what had been left behind down there.
They didn't comment on his expression, glaring down on the entrance to the Underground. They understood, better than probably anyone else, how many bad memories were buried deep in the mountain. Though it had led them to a new family and a happy ending once all was said and done, this hole had still been the starting point for a journey that had killed them countless times. They were scarcely any more eager than he was to jump back down.
"Hey! Are you two ready to go?" Kaila, the expedition leader, called to them from where the rest of the team was gathered a few yards away, near the other side of the hole. Sans jolted, shaking himself a bit before shooting a wide grin over to the team.
"Who us? We were bone ready, pal."
Frisk giggled as they took his hand and walked with him over to the others, double checking that their climbing gear was strapped on securely over their lab coats. A pale blue flush spread over Sans's cheek bones. He still wasn't used to...well, to how affectionate Frisk was. Not that he was complaining, of course. The kid was like family to him.
After an hour of slowly and carefully climbing down the hole into the Underground, Sans wished he'd just taken a shortcut. If it'd just been Frisk and Alphys with him, they'd be half way to Snowdin by now. But his shortcuts were a little far out there, even for monsters, and he didn't really want to advertise his abilities to the humans.
When their feet finally touched down on solid ground, there was a collective sigh of relief that swept through the group. Sans glanced around. Nothing looked out of sorts yet, but then again, they'd only just arrived. He cast a look over to Frisk. Their back was ramrod straight and their mouth was drawn into a tight line.
"Hey kid, are you-" he started, only for Kaila to interrupt him with a loud clap.
"Alright everyone! We've got a lot to do and a very tight schedule to get it all done in, so let's get started. Max, take a soil sample from here. Yareli, you get that camera set up and take stills and full spectrum photos as we go along. I want this place fully documented."
Alphys shifted on her feet, her claws carelessly picking at the sleeve of her lab coat. " A-as far as the Ruins go, I'm n-not very familiar with them. Fr-frisk is the only one with us right n-now that's been through them. Should they lead a few of us on ahead to m-make sure everything is clear?"
Kaila nodded and looked to Frisk with a raised eyebrow. Smiling, they gestured to Sans. "There are some puzzles I remember up ahead. Sans and I will go make sure it's safe for everyone to come along," they said.
Kaila frowned and crossed her arms. "Just the two of you?"
Sans shrugged and threw an arm over Frisk's shoulders. "Sure, why not? I'll keep the kid outta trouble."
The head scientist eyed them warily, but ultimately waved them off and turned to talk to Alphys. As soon as no one was looking, Frisk seized his hand tightly and began pulling him down the path through the Ruins. Their fingers were trembling, making Sans's bones rattle against each other. Once they were far enough down the corridor that the rest of the team wouldn't be able to see them, Frisk's grip tightened even more and they started to run down the path.
"H-hey kid, what's the hurry?" He asked, tripping over his slippers to keep up.
Frisk's breath was coming in short, quick gasps through their teeth and their eyes were glued forward. "Something's wrong," they hissed, yanking him forward, urging him to go faster. Sighing, he jumped forward and pulled the human against him.
"Shortcut," he explained before ripping them through space.
They landed hard in a bed of soft, decaying golden flowers. The smell was so strong that Frisk gagged beside him (of course, that could have POSSIBLY had something to do with the teleporting, too). Sans looked at his hands and groaned. His bones were covered in the sticky decay of the buttercups.
"Huh, all the flowers are dead. We better get to the root of the problem, huh pal?" He joked, looking up at Frisk for a reaction. He froze when he saw their expression though. Frisk was staring with hide horrified eyes at the flowers around them, holding a few rotted petals in their hands. They were shaking violently now, and their breathing was ragged and uneven.
"This is wrong. They should be alive. Something is horribly wrong," they insisted.
Sans tilted his skull at them and cautiously took ahold of their arm, trying to calm them down. "Hey, hey buddy. They're just some dead flowers. That's not too unusual. Doesn't mean the world is ending."
Frisk shook their head, grabbing onto Sans's hoodie sleeve like their soul depended on it. "Not these flowers, Sans. These are Asriel's flowers. Something's not right. You feel it too, right? I know you do."
The white lights that served as pupils faded from Sans's eyes as he looked away and chuckled without humor. He stood without answering, offering a hand to help Frisk up, which they accepted, still shaking slightly.
"We both know there's been something going on down here since everyone left," they murmured, brushing the last of the dead flower petals from their hands.
Sans was about to, reluctantly, agree, but something caught his eye at the corner of the cavern. Th shadows there seemed to be twitching, convulsing around themselves. For a second, he could have swore he saw a line of red coding, too.
He looked to the kid, who just nodded, wide-eyed at him. They'd seen it too. "C'mon," he said, taking the human's hand in his own this time, "let's keep moving."
They got through most of the Ruins unmolested. The puzzles were simple, and most could even be turned off by the switches on the walls. Every couple of rooms or so, though, they'd notice more of those strange anomalies in the shadows, or on the walls. Like reality wasn't quite lined up with itself. More than that, there were somethings that just shouldn't have been there. Sans didn't point out the double shadows he caught sight of to Frisk. It'd just freak the kid out more.
There was one other thing that was off, too. The SAVE points were gone. That sort of made sense, Sans thought. With no immediate threat to the human's life, there wasn't much need for the SAVE stars to offer RESETS. He wanted to be relieved. He wasn't.
Once they reached Toriel's old home, Frisk suggested they go back for the others.
"Don't ya at least wanna have a look inside first?" Sans suggested.
It happened right as he was reaching for the doorknob: the whole house glitched. It was like static, with the whole top half of the house spasming on and off center rapidly for a couple seconds, with a horrible ripping sound, before it settle back to normal. Frisk stumbled wilding back from the door, pulling Sans with them.
"Shit," he swore, instinctively putting a hand out in front of him and the kid, ready to attack.
Frisk was clutching at the back of his hoodie, frowning at the house. "The only way out of the Ruins is through Toriel's house. What do we do with it like this?"
Sans started walking backwards, hand still slightly raised towards the house in suspicion. "Well," he mused, "whatever these anomalies are, they don't seem dangerous on their own. I figure we'll just have to bite the bullet and go through once we've got everyone together."
Frisk chewed their lip. "Don't you think we should test that theory before we lead them through?"
Sans squinted at them. "How?"
Without an explanation, Firsk ran over to the tree in front of the house, which was glitching a bit on one side, and tentatively reached to touch the anomaly. As soon as they did, the piercing tearing sound came from the glitch and the whole section of the tree spasmed out of space violently, before it settled completely and left the tree unmarred, with no mark to show the glitch had been there in the first place. Frisk sighed deeply in relief and drew their hand up to their chest, grateful they hadn't lost the limb in their little experiment.
"Alright," they said, "let's go."
Just before they rejoined the group, Frisk had asked Sans not to mention the glitches. They said they didn't know why, but they had a feeling that the others wouldn't notice, and that they shouldn't tell them. Sans knew better than to expect a clear explanation- neither of them really understood what was going on- but he trusted the kid's judgement. Turned out that was a good call. As they walked back through the rest of the Ruins, no more anomalies showed up. And, even as they worked their way through the rest of the Underground, they didn't see anymore of the strange glitches along the way. Still, the weird feeling coiled up inside of Sans was getting harder to ignore with each passing hour. And, despite how hard they were clearly trying to appear as if nothing was wrong, he could tell Frisk was feeling off, too.
Sans and Frisk mostly left the field work to the research team, opting to lead everyone through the puzzles and act more as guides than anything else. That gave them plenty of time to check each area for signs of more anomalies, or for any indication that Flowey might be around. The soulless flower had been disturbingly absent throughout this little excursion. They both knew that, if he was still around, he must have seen them by now. If that was the case, he was probably following them, too. But they hadn't seen any sign of him, or even sensed him nearby. Sans couldn't tell if that was a good or a bad thing, based on Frisk's reactions. They looked like he'd d felt everyday down here: like they were just waiting for everything to go to shit at any second.
On the third night back Underground everyone was camped in the old castle. The plan was to return to the Surface in the morning, so by the time they reached the research center (a good three hour drive away), it would be just about noon. The team was mostly set up in Asgore's old room and the room that had been labeled as under renovations. Alphys had opted to take the couch in the living room. Frisk had asked Sans to stay in Chara and Asriel's old room with them, and he'd agreed. The kid seemed even more on edge tonight, despite how close they were to the door that lead back to the Surface. He looked over at them, curled up facing away from him in Chara's old bed. He frowned, wondering if sleeping in the same bed that that demon child once had would give them nightmares.
As if reading his mind, Frisk chose that moment to roll over in bed and stare at him, clearly wide awake. Startled, his left eye lit with blue flame and they both hissed at the sudden light.
"Aw geez kid, you almost put me into cardiac a-rest," he complained, pushing his palm into his eye socket as the blue light faded.
"Sorry," they murmured into the bend of their elbow, still watching him. Slowly, as if afraid someone was listening in on them, they whispered across the room: "Did you see them, too?"
Frisks eyes were wide and afraid in the dark, straining to focus on him for some form of comfort. With a sigh, Sans pulled himself from the small bed and went to sit with the human. This was really starting to get to him. He wasn't used to seeing Frisk afraid. After all, this was the kid that had gotten through the Underground without hurting a fly, and then befriended and liberated an entire civilization. Not to mention how many times they'd been killed along the way. In all that time, he'd hardly seen the kid flinch in fear. They must be really bothered to be reacting like this.
They scooted back on the bed until they were pressed against the wall, and sat up. They wrapped their arms around their knees and slouched forward.
"You noticed them, right? The shadows are twitching again in here," they whispered.
Sans sighed. He'd noticed them, alright. The anomalies had returned , subtle and unnoticed in the shadows. He wouldn't even have seen them if he hadn't been looking. It was just a sort of shift in the darkness- a split second where everything would jolt sideways and the shades of black wouldn't quite fit together. None of the humans had noticed it, besides Frisk, and neither of them had mentioned it aloud until now.
"Yeah," he admitted, "I saw a couple strings of code once we got to the Core. Doesn't seem to be too bad. 'Sides, we'll be outta here again tomorrow." He tried to sound as optimistic as possible, even with his own feeling of dread building as the night went on.
Frisk chewed their lip. "The golden flowers are all wilted," they pointed out. " The others just thought it was neglect since everyone left, but I saw that it bothered Alphys as well. As far as we know, Asr...Flowey is still down here somewhere. Even if we haven't seen him. Could he have something to do with it?" They visibly flinched when they corrected themselves on the soulless flower's name, still having a hard time separating the murderous flower from the sweet monster prince he'd once been. But one of Asriel's last requests had been for them to not think of the flower as being him, so they tried.
Sans slouched back against the headboard of the bed and wrapped a comforting arm around Frisk's shoulders. He leaned his skull against the kids hair and closed his eyes. All this anxiety was tiring him out.
"There's nothing we can do, for now," he reasoned. "Let's get back to the Surface. If you want, maybe we can come back and check out the anomalies later. Just you and me. But maybe...maybe it'd be better to leave the Underground be, ya know? Let it decay, undisturbed and empty. It took a whole lot to get it that way, after all."
Frisk didn't respond, and Sans couldn't say for sure how long after that they both fell asleep propped up against each other. Sans dreamt of blackness and glitches, streams of red code, and skeletal hands with holes in them.
Sans snapped awake violently to the sound of someone rapping on the door. It was one of Kaila's research assistants, telling them it was time to get up and packed for the Surface. Relaxing, he sucked in a few shaky breaths through his teeth and looked around. Frisk had slip down through the night, ending up half curled under the hallow of his ribs. Stifling a chuckle, he gently shook their shoulder.
Frisk groaned and smothered their face into his hoodie. "Five more minutes," they grumbled. Grinning, Sans wrapped both his arms around them and hoisted them up as he stood, making them yelp and grab at his shoulders and ribs.
"Sans!" they shrieked, one arm waving frantically at the ground.
"What? Kai said it was time to get up so..."
"Sans, no."
"Sans yes."
It took a little over an hour for everything to be checked and secured. Everyone regrouped in the throne room, with Alphys coming in last. She seemed a bit tweaked, like she hadn't slept all night, and Sans wondered if the whole thing with the flowers dying had kept her up. Frisk had stayed pretty close to him since they got up, though they managed to refrain from clinging to him in front of the other humans. They knew that, as an ambassador, they had to maintain an image of independence. Still, they shot Sans a concerned look after they caught sight of the dark shadows under Alphys's eyes. Sans nodded almost imperceptibly to them. They were almost home, he thought. It'd be fine once they got back. But those thoughts in his head came in Frisk's hopeful voice, and were barely covering up his own inner monologue. The one he'd tried to leave behind after their first weeks on the Surface. The voice that whispered that everything was pointless, that he was helpless and should be prepared for the worst, because that was all he'd ever get in the end. He clenched his jaw tight and tried to ignore the echoes of the traitorous thoughts in his skull. He was used to it. He had to be strong now for Frisk, no matter how nervous he felt.
The door that had once lead to the Barrier corridor now lead to a long path of black and white stairs, leading up and out onto the Surface, the walls turning to stone the higher up one climbed. Sans had only seen it once before, when everyone had climbed to freedom nearly a year ago. Now, he followed behind the humans and Alphys, who hung back slightly with he and Frisk. Frisk was holding his hand now. Almost crushing it, really. They'd started to tremble, wide eyes darting all over the walls of the corridor. Even Alphys was muttering to herself, fidgeting more than usual and nearly tripping over her own feet more than once.
They were more than three quarters of the way through the corridor before a feeling hit Sans like a ton of bricks, nearly bringing him to his knees. His bones felt like lead, and the space around them like jelly. He could barely move. Frantically, he squeezed Frisk's hand even tighter in his, refusing to let go not matter what was going to happen. He heard a choked sob come from Frisk, but he couldn't stop looking ahead. Alphys and everyone else had continued walking like nothing was wrong. He tried to call out to them, but no sound would come out. He heard Alphys keep muttering to herself, and caught a few stray words: "The flowers...no response...determination...decay...photon...negative."
The whole corridor glitched, space and time seizing sideways and down, cracking and screaming. Streams of red coding filled his vision, and all he could feel was Frisk's hand heavy in his. Then there was blackness.
"PHOTON READINGS NEGATIVE...WHAT DO YOU TWO THINK?"