Papyrus had always been a kind of annoying brother. Everything always had to be his way…Even when his way was completely wrong and absolutely stupid. Sans had loved his brother though; since the two were baby-bones he had doted on Papyrus doing basically everything he could to keep the louder skeleton happy. Sans was kind of a jerk sometimes, but Papyrus really was his whole world. He didn't have many friends, Papyrus didn't either, at the end of the day they really only had each other.
But now, Sans had nothing.
The house was quiet now. No pesky younger brother yelling at him to feed his pet rock or pick up his socks. The house didn't smell like burning pasta and there was really no reason for the fire extinguisher Sans had placed under the giant sink anymore. Papyrus was dead now. He wouldn't be cooking or yelling or becoming a member of the royal guard or laughing or making friends or … Sans felt himself choking up so he pushed away the thoughts.
The human had progressed far in the Underground since Papyrus's murder; last he'd heard they'd been slaughtering monsters in Hotland left and right. The thought made Sans sick to his stomach. Maybe if he'd done something when the human was here in Snowdin…Maybe if he'd been the one to fight them instead of Papyrus…He could have prevented all this. He could have been the hero that nobody ever expected he could be…
Sans was the only person left in Snowdin now. Everyone else was dead or had fled though he found himself doubting that anyone who fled had gotten very far. Papyrus' murder had sparked a much bigger massacre in Snowdin but for whatever reason the human chose to leave him. Granted, they might not have known he was barricaded up in his house waiting for Papyrus to rush back in begging for help in capturing the human. Being the only one alive was kinda lame. Kinda lonely. Sans didn't enjoy it much. There was no one to force him to do his sentry work (not that it would be very helpful anymore) and there was no one to nag him, but that also meant there was absolutely nobody to talk to so Sans was stuck completely alone with nothing to think about but the circumstances of his brother's death.
It wasn't supposed to go like this. That's what the little voice in the back of Sans's head kept repeating. Something was wrong, very wrong. Sometimes, Sans would have dreams about the murderous human ... They weren't really the dreams that would be expect. He dreamt of the human and Papyrus running around in someone's sunny backyard catching butterflies, cooking together, laughing; he dreamt of tucking the human in when they passed out on the couch, ruffling their hair and watching them grin, making the most awful puns and having them absolutely roar with laughter. The dreams just made him feel emptier inside. A part of Sans – an embarrassingly large part – hoped that his dreams were reality. That any moment he'd wake up to be on the surface with Papyrus alive and the human his friend. Everything would be okay.
Sans often found himself wondering how he knew what the surface looked like. He'd never seen anything like the place in his dreams and it just seemed too vivid to be made up. It was his dreams that spurred him back into his studies. He wasn't sure why he had ever stopped in the first place; one day he had just woken up and everything just felt … wrong … like he couldn't continue any of his experiments. That set aside, jumping back into the ol' sciencey saddle he quickly realized what was happening. Somehow…The kid was messing with the timeline.
Sans became obsessed with his dreams after a while. He was convinced they were a window into another timeline. A timeline where he had his brother, where he was a good brother, where he had protected Papyrus like he had always sworn too. Sans needed to get to this other timeline. He needed to make things right for Papyrus. He would fix it…He had to fix it…
That was why he sought the human out and fought them in the final corridor. If he could beat them…Maybe…They'd RESET. He'd get his brother back. He'd get a second chance. The human was a monster in this timeline but maybe in another they'd be his closest friend. If that didn't happen … well … at least he'd get to avenge his brother.
The human grinned at him, a feral evil grin very unlike the one he'd been dreaming about for months. "You should've stayed out of my way."
Sans shrugged. "if i did that you wouldn't reset, right frisk? i need you to reset." The human never told him their name but they seemed to respond to Frisk, looking up and laughing softly.
"Frisk isn't here anymore."