"H...help!!! Toriel! Papyrus!! Alphys! Undyne! Asgore!! S... somebody, help me!!!"
– Frisk after being attacked by Sans in the Genocide Route.
Frisk is the main protagonist of Swaptale. They are the eighth and final human to fall into the underground.
Frisk is about to spare Flowey and complete the Neutral Route. But as they press their Mercy button, their hand appears over the Fight button. When they look up, they see Sans (who thinks they are still Chara), preparing to attack them.
After getting their LV lowered to 1 HP by Sans' Gaster Blaster, an extremely confused Frisk calls out to their friends for help... but nobody came.
After a few moments of his own confusion, Sans realizes there has been a mix-up in the timelines. Once he is sure that the Frisk he is facing isn't Chara, Sans takes them to Grillby's, abandoned after Chara's rampage. There he explains to Frisk that he has had dreams about them (Frisk) where they freed the monsters from the underground and that Chara was not that person. This Frisk is the one that Sans had been dreaming about.
When Frisk begins to understand that they are in Chara's timeline, they realize that Chara is in their timeline. Sans tells Frisk that he knows how to get to the other timeline in order to save Frisk's friends. At first, he is reluctant to do it, but he decides that he has to.