one day paps decided he was gonna try and make a bone bridge across the snowdin river and while he was walking, a piece of ice cut through the bone bridge and paps was getting swept away, as soon as sans heard paps, he ran and used his gravity powers and threw him out of the river and sans swore to protect paps from any dangers. so paps decided to see how far sans would take it and had undyne burn his spaghetti so sans impaled undyne with bones and she was missing but nobody knew what happened, and paps didn't tell anyone because he didn't want sans to get taken to jail, so whenever paps was bullied sans got a little more dustier until people started noticing and when the truth came out, paps was attacked and k!lled which made sans go on a rampage because he was already losing his sanity, and leaving the human till last to k!ll...
he wears paps scarf in rememberance of him and why he started this to give him a reason to not regret it all, it would take place in a non-underswap au.