Author's note: Italics are wingdings because I'm not very creative. And now, into the story!
Sans stumbled and fell forward, his arms in front of him to brace his fall. But he never hit the ground. In a sudden panic, he opened his eyes, and took in everything around him. Or lack thereof.
"The hell?" He asked, and was startled when he did not hear his own voice. He glanced around again, trying to find something for him to focus on. Anything. But the world around remained black and featureless. He stared down, or what he assumed to be down, and realized that he was not standing on anything. He reached down to touch the ground, but felt nothing.
After a minute of floating through the empty space did he decide to activate his magic, wanting some kind of light. He regretted it instantly as a flash of pain shot through his eye. Sans looked down at his hands when he saw movement that was not his own and flinched back when he saw his hand glitch a few inches to the left then go back into place. He touched the hand to his eye and was reassured when he felt the touch, but frowned when the pain in his eye did not dissipate.
"You should not do that." Sans heard, or rather, consciously acknowledged the words as he spun around, trying to identify where the voice had come from.
"It has been a while." The voice continued, and Sans glanced around again, but this time caught sight of something, and yelled in surprise when a face appeared a few inches from his face.
"W-who are…?"
"Surely you have not forgotten me already." The face backed away a few feet, hands materializing out of the space around him and coming together in front of him.
"I-I...but… Gaster?" Sans stumbled over his words, astonishment and disbelief causing his mind to struggle with thought.
"yEs SaNs," Gaster answered, and Sans flinched at the sound of his voice. It cracked and fluctuated with every syllable, as if not being able to focus on a single pitch.
"But, how are- I saw- you died!" Sans could feel tears welling up in his sockets as the memories of that time were bought back.
"I thought I had too," Gaster sighed, the sound a sharp static. Sans took in the other's appearance, only able to make out the hands and face. They seemed to be melting.
"Then how…?" Sans let his words trail off, then he sucked in a sharp breath as his eye spiked in pain once more. The colors from his activated magic streamed off in trails around him, and he looked down to see his soul doing the same.
"You must leave now!" Gaster's voice rose in volume, rising to a screeching that continued well past when he finished speaking. The sudden change in volume caught Sans off guard and he yelled out in pain as his skull seemed to vibrate with the echoing words, made almost indistinguishable now.
"LEAVE!" Sans could hear Gaster yell over the cacophony around him. Everything became unbearable, the screeching from the nothingness around him puncturing into his very being and burning his bones.
This was it. He must be dying. He wished it wasn't so painful. The world glitched.
The ground was solid beneath him. That was Sans' first thought. The next was that his skull felt wet. And not from the ground. He heard a faint whining coming from above him.
"Sans?" Greater Dog whined, then proceeded to lick his skull a few more times, trying to rouse the skeleton. Sans did not have the energy to move away at the moment, nor the willpower to tell him to stop. His soul still burned, albeit to a much lesser degree than what it was a few moments ago. What had happened?
"I called Captain. She will be here very soon. She will know what to do," Greater Dog seemed to be mumbling to himself as Sans refused to stir from his prone position on the ground. The mention of Undyne, however, made him move into action, although slowly, his bones feeling weighted down, as if filled with lead. His eye also burned as he opened them and took in the wet grass in front of him. He closed them again and groaned as he heard the echo of the one person he did not want to see right now.
"I swear if anything else has happened since-"
"Undyne, please slow down a little!"
"Sans!" Said skeleton moved back into action again as he heard his name called out in surprise. A few more seconds passed until the upper half of his body was lifted from the ground. He forced his eyes open once more, hissing quietly at the pain and noting the glow coming from it. He blinked the magic away, trying to focus on his brother, who was staring down at him, a worried frown replacing his usually enthusiastic features.
"Is he alive?" Undyne walked up behind Papyrus, and Sans could feel a headache forming already.
"Yes," Papyrus answered, not taking his attention from his brother.
"Heya, pap," Sans said, trying for a smile, but probably getting something resembling a grimace.
"Hi Sans. Can you stand?"
"Um, I wouldn't count on it, but I bet I could sit alright," Sans pushed himself from his brother's steady hold and, after catching himself in the wet grass, steadied himself and stared up at his brother.
"Sans… brother, what… why did you leave? What happened here?" Papyrus' tone switched between worried and upset. Sans was not sure which one hurt him more.
"It's a-"
"No brother. Do not tell me 'it's a long story'. I need to know what happened so we can help," Papyrus cut Sans off angrily, then dropped his tone for worry once more. "This is the second time in a 24 hour period that I have found you unconscious. I am worried, Sans. I do not know what is going on, and I am afraid of what is happening to you. I cannot go through this again." And the last part made Sans' heart break.
"Pap...bro…"
"Sans!" A groan from the skeleton at the call of his name indicated he had heard. "Greater Dog just got through explaining what happened. Considering that you seemed awfully excited to run toward this thing, you'd better have a good fucking explanation for doing so."
"Ugh... Undyne do we have to do this right now? I just got back from-"
"No Sans. One of my men and a civilian have disappeared into thin air and I want know why. So if you know, then you better fucking tell," Undyne had stormed up beside Sans and now stood over him, glaring down in all of her fury. Sans rubbed his temples with one hand, trying to stop his growing irritation.
"If I knew what the hell was going on, I would be more than happy to tell you, okay? I just jumped into a black hole in the middle of this fucking room for your guard and shyren. I am in-" Sans paused in his rant when he heard a low beeping coming from behind him. He turned an irritated glare at the object in question and came face to face with Alphys, who squeaked in surprise at the movement and fell back onto her tail.
"I-I am sorry, Sans. I was just- I got a notification that your… that your magic was, um... " Alphys trailed off awkwardly, looking down at her phone, which was still beeping steadily. "I, um, a-also caught another strange signature in the a-area. B-but it cannot be correct…" Alphys mumbled then began typing into the phone.
"Alphys, what the hell are you trying to say?" Undyne cut in, her arms now crossed impatiently across her chest and staring down at her significant other in mild irritation at having her conversation with Sans interrupted.
"W-well, Sans' magic is… well, it changed since the-the last time I took a reading a f-few hours ago," Alphys finally continued, fixing her glasses and moving closer to Sans again, passing the phone over his chest. There was a soft 'ding' as the scan was taken, then Alphys did the same with Papyrus.
"The heck you need pap for?" Sans inquired, relieved the tension was taken somewhat off of him.
"W-well, I took the magical signatures of all of our closest friends, to- to test the program efficiently. Yours was the only one I've been actively u-using it for, though." She read over the scan when it had completed on Papyrus, then turned behind her and made the same scan into the air.
"So…?"
"So, when I came into the room, I h-had received a notification from both you and your brother. I-it can detect magical signatures within a hundred foot perimeter. It is still in the prototype phase, so it will have a larger radius later on. If I were insert a-"
"Alphys, I'm sorry, but can you get to the point?" Undyne urged, her foot now tapping impatiently.
"O-oh, sorry. Well, when we entered the room, the device picked up Papyrus, b-but he had been next to me the whole time, a-and seemed unchanged. I looked closer, and the app was reading two separate magical s-signatures. Which it has never done before. I-I checked it over. It was r-reading it from… um.. From you, Sans." Alphys finally finished weakly, her previous enthusiasm dying with her words.
"Okay… that's all fine and dandy, but what does that have to do with our current situation?" Undyne finally spoke up.
"I don't- I'm not sure. It could just be a glitch, o-or it could be-"
"Do you think it might be from the rip I just came from?" Sans interrupted, his mind now working to solve this new puzzle.
"Oh, yeah, that brings us back to why I was pissed at you in the first place. What the hell happened down here?!" Undyne's eternal rage spiked again as she was reminded of the the reason one of her men were missing.
"Look, I don't really know, okay? Can you just… can you give me five minutes to process the shit I just experienced in peace please?" Sans shot back, and a quickening beeping could be heard behind him. "and can you turn that damn thing off for a minute?!" Sans shot at Alphys, who flinched away under his gaze.
A few tense moments passed, the beeping continuing. Finally Alphys reached her hand up and touched right below her eye.
"U-um… your eye," she said. Sans reached up and mirrored her action, wiping right below his left eye. He pulled his hand back and stared dumbly down at the blue liquid that was covering the phalanges. He was startled when he felt a soft cloth under the eye and pushed away the gentle touch of his brother angrily.
"You know what? I need a nap," Sans then activated his magic.
"Sans, don't-" But he was gone before Papyrus could finish his sentence.