Aftertale is an AU where Sans attempts to save a new timeline from Chara.
About the AU
Aftertale is an AU where Sans injected himself with Determination to defeat Chara and leaves the timeline when he was turning to dust, becoming stuck in the void with Frisk.
His SOUL was split, and the Sans still within the Underground holds most of it, while the original Sans only has a 9th of a SOUL.
The new timeline’s Sans kept experiencing nightmares of a genocide run, eventually meeting the human and confronting them at Grillby’s about the dreams he was having. He discovered this human was Chara, who he erased from the timeline only to be pulled out of his to meet the previous Sans who calls himself “Geno”. There he learns about everything that is going on, now he must figure out a way to stop Chara before the world ends for good.