SlayerTale is in AU in which the Sans of this universe becomes a Protector of Other AUs.
After 99 Genocide Runs, Frisk is now a mindless slave to Chara. His wish is Frisk's command now. Sans has had enough of watching Frisk kill him and his friends over and over. Sans had managed to take a SAVE Star from earlier in Snowdin. He absorbed it, and was given immense power.
Sans's jacket turned yellow, the stripes on his pants became yellow, his slippers turned into brown boots, he gained finger-less black gloves. He gained a gold tooth, and his eyes became yellow. One was a yellow circle, the other was in the shape of a SAVE Star. His stats skyrocketed. Sans, with this newfound power, decided to take Chara.
As Chara entered the Judgement Hall, Sans was nowhere to be found. Sans appeared behind Chara and started attacking. Chara stabbed Sans in the heart. Sans thought it was over. But Sans only lost one HP. Sans then stuck his hand in Chara's chest, intending on taking his SOUL. As he yanked his hand back, he instead separated Chara's SOUL from Frisk's. Everyone was confused. Sans then attacked Chara. Chara said, "D-don't hurt me Sans!! Grant me mercy!! I BEG of you!!!" Sans said, "You... who are without mercy, now PLEAD for it?! No". Sans then used a Gaster Blaster on Chara, killing him.
Sans walked up to Frisk. He whispered, This is the part where you reset. Frisk then reset. Frisk saw Chara, who relinquished control to Frisk. Even though the timeline reset, Sans was still wearing his yellow clothing. He realized that he now existed outside of a reset. Frisk did a Pacifist Run and got everyone to the Surface.
Sans was then visited by Error Sans. Error was about to destroy the AU, but Sans attacked. After breaking a few of Error's ribs, Error ran away going, "You haven't seen the last of me!!" Sans was then visited by Ink Sans. As Sans was about to attack Ink, Ink raised his hands in the air said, "Wait! Wait! Wait! I'm a friend! Ink said he saw the fight between him and Error and wanted to recruit Sans. Sans asked why Ink needed his help. Ink said that he was a good candidate for a Protector of other AUs. Sans agreed. Ink told dubbed this Sans, "Slayer Sans", as he was in the AU SlayerTale.
Sans was brought to the Doodle Sphere. Sans said that he wanted a weapon. Ink, although confused obliged. Slayer Sans drew a weapon of his own design. Ink brought the weapon to life. This weapon was a combination of an Axe and Scythe. It also had a wooden stake on one end. Sans called this the "Slayer's Axe."
Sans still lives in SlayerTale, but he is still often called for duty. While Ink and Dream take on external threats, like Error Sans or Nightmare, Sans focuses more on internal threats to AUs. He likes to think of it as "Protecting them from the inside out." What he does is find an especially evil person and rips out the evil controlling the person. Slayer still helps when an AU is under attack of course.
- Slayer Sans's weapon is actually the Slayer's Scythe from Buffy the Vampire Slayer.