Sans stood rigid as he saw the human disappearing into the fog, to the Waterfall. Papyrus's dust had formed a neat little pile in the snow, and was slowly beginning to get covered. He was too late. He was coming to warn Papyrus, to help him fight. He knew that his brother was far too kind, had far too big a heart to let the human die. To even fight her. It would be easy for the little demon to kill his brother.
To kill his only friend.
The only one who would hug away his night-terrors. The only one who was able to understand why the resets would happen. The only other one who wouldn't be impacted by them. Papyrus seemed tough, sure, but at home, he was nothing more than a kind-hearted old fool. He would never let anything happen to Sans, and neither would he. Papyrus didn't let the resets get to him, not like Sans. The skeleton had always thought of them as "more time to do things I like to do." Sans had seen them as hell.
Sheer hell.
Now his brother was dead, lying in a pile of ashes. In a pile of gray dust. The same dust he had seen on the human's hands. Of course, Sans had thought nothing of it, but seeing his brother like this... he had to something. He had to end this reign of terror. He had to kill this human. He knew she had the power to reset the timeline. That's why it had been happening. He knew she had that power, but he could slow her down enough, maybe make her reset the whole thing, go for a different way to go about things. Go for a different ending to his brother than this.
Something yellow caught his eye. A flower? he thought tentatively. What's a flower doing in Snowdin...?
The flower had a simple smile, and two beady eyes. Those eyes had the same, soulless expression he had seen in the human. For a moment, though, they flashed with something as they landed on Papyrus's dust. Recognition? Sadness? Sans couldn't tell.
"After all this time I spent building up his confidence..." the flower muttered. Sans let out a broken whimper. This was the flower Papyrus had been talking about, he just knew it.
The flower looked up, saw Sans, then disappeared beneath the ground.
As much as it pained him, Sans wished the human not to die from here. Not until they made it to himself. He couldn't relive this anymore. Not again. He couldn't stumble upon Papyrus anymore. He couldn't hear his brother's final words. He couldn't... he just couldn't...
Sans replaced the wide smile to his face, and set off for the Barrier.
He would stop this human.
He had to.