Sans awoke to the sound of the cell door opening. He looked up to see the alternate Sans standing there, but he wasn't holding any rations for him. It made him look oddly bare. He just stood with the door wide open, sweating profusely.
"Come on." He said quickly, and looking around like he was about to be attacked from any angle.
When Sans didn't move, the other spoke again more hastily.
"Come on, I'm getting you out of here."
Sans knit his brows together looking the other skeleton up and down before chuckling.
"Nice try." Sans said turning over.
"I'm being serious, you idiot!" The doppelganger exclaimed, before taking a deep breath.
"I know you don't trust me…"
"What gave you that impression?" Sans interjected.
The other made an agitated noise, then continued, repeating himself slowly this time.
"I know you don't trust me, but I want to get you out of here. Look, if we hurry I can get you into my lab before Papyrus is back from sparring with Undyne."
"And why should I trust you?! The last time I did, I ended up in here!" Sans said angrily.
"Shut up! Just listen!" He exclaimed, before trying once again to compose himself.
"Seeing you, seeing me, seeing how I used to be, has made me realize this. It's made me realize just how unrecognizable everyone is, especially Papyrus. Before, he wouldn't hurt a fly, much less a human, but after he was injected with determination… if someone like Papyrus could change so dramatically, then what can be said about the rest of monster-kind?"
There was a brief moment of silence, before the other sans continued.
"The determination in our blood, it craves more LV but there is no one left to kill. All the humans are dead, and any monster that wasn't able to obtain enough LV or get protection from someone with high LV was dusted. So, where can we find new low level humans and monsters to obtain LV?"
Sans didn't understand what the other was getting at, before the realization hit him.
"My timeline."
The other Sans nodded grimly.
"I'd been trying for a while now to take shortcuts to other timelines, to little success. But, using your magic like a passcode, it would be much easier to find your timeline and get there. Papyrus has been very keen on the idea of increasing his LV even further, and your arrival only made him want it more. I've been trying to stall for time, but I can't, much longer. He wants to hop timelines as soon as possible. He wants to become a God."
The two sat in silence for a while. Sans still didn't trust this other skeleton, but the thought of his friends and everyone he ever knew potentially being dusted because of him, made him feel extremely ill.
Sighing in resolve, Sans stood up on shaky legs, before facing the other.
"Okay, but before we go, I have one question."
The other Sans stood still meeting his gaze, he wasn't sweating or shaking for the first time he'd ever seen him.
"If everyone went LV crazy when they were injected with determination, then why do you still have such a relatively low LV?"
The other sighed, and turned away from him.
"I was one of the first who was successfully injected with determination. Alphys had just figured out how to do it, and I volunteered to be her first test subject. The two of us were the first. After that, she was quickly able to hone her method and make the amount of determination a monster could take much higher.
Look, we better get going. Here." The other took off his dark sweater and handed it to Sans.
"Can you walk?" He asked once Sans had pulled the cloth on and zipped it up tight.
"Yeah, I think so...tibia honest." Sans gave a small smile.
"You're a real comic, Sans." The other laughed. The two stout skeletons made their way out of the shed and headed for the lab. Heading around the back of the house, the native Sans opened the door, ushering the other in. He looked around carefully making sure no one else was nearby to spot them. Sans entered the lab, and just like the house, it looked nearly identical to his own. The other booted up his machines and began typing into his computer. He then went over to the corner of his room, where a tarp hid something underneath. Pulling it off revealed a fairly plain looking door, but Sans knew there was more to it than met the eye. The other quickly went back over to his computer typing on a few more keys.
"I need you to put your hand on this scanner and discharge some magic." The red and black clad skeleton said.
"Shouldn't you take this collar off first?" Sans asked.
"I can't, Papyrus has the key, and trust me, I've tried to get it before. You might be able to get it off using the magic from your own Papyrus" The other said.
"Might." Sans echoed quietly.
He approached the scanner and laid his hand upon it. Sans focused deeply on trying to muster up his magic. It felt like pulling a safe up a well. It hurt too. The spiky thorns of resistance stabbing into his soul. Sans was sweating by the time he heard a satisfactory ding come from the machine. The door lit up then. His home lay just on the other side.
"SANS, WHERE ARE YOU?!" A voice shook from outside.
Both of the skeletons jumped in surprise.
"Shit, he's here! Go! Quick, before he-" The doppelganger cried before the door to the lab was flung open.
"JUST WHAT DO YOU THINK YOU'RE DOING?!"
Sans turned and ran then. He didn't look back. He hurled open the shortcut door to the sounds of indistinguishable screaming behind him.
I got quite a few requests to continue this. I'll admit it's not a story I'm super passionate about, but I can give you this chapter that I've been sitting on for a long time.