So fallenTale right? Split into three routes this follows the destruction route:
Route goes on like a normal passive route. Right before Frisk is supposed to defeat Asgore something happens. We later find out that Chara (who is separated and revived in this au) revived Gaster and teamed up with Paint to destroy the world of fallenTale (as Chara has the evil stereotype in this au help-) basically the world slowly crumbles from the inside out and the CORE slowly collapses and eventually explodes everything after Chara kills Toriel and a few people out of boredom. Everyone dies with the subtraction of three characters, Flowey, Frisk, and Sans, who watched his brother die earlier and is sad. Instead of having Frisk RESET, Sans decided to split his soul in half to save Flowey and Frisk and they both teleport away, leaving Sans to die. Only after the explosion he doesn’t die and instead now wanders the cursed and destroyed au, soulless. Ruby (who has just escaped from prison) accidentally teleported to FallenTale and meets with FallenTale Sans (who goes by Fallen) Fallen now has to steal souls to feel emotions (which doesn’t really make sense??? I also never really explored into that and after this it’s just kinda forgotten about, what whattt…)