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Underswap is an AU where all of the characters' roles are swapped, as well as their personalities, though some quirks tend to stick in places, or are modified. Sans is the excitable, confident, extremely optimistic human hunter, while Papyrus is the laid back, protective bro following Chara (who is swapped with Frisk). Other swaps in this AU are Asgore and Toriel, Alphys and Undyne, Napstablook and Mettaton, Grillby and Muffet, Burgerpants and Nice Cream Guy, and Flowey and Temmie.

The plot of Underswap revolves around each character from the Undertale universe being swapped with other characters, such as Sans' and Papyrus’ personalities being swapped (although they keep the same names, so what we consider Sans to be as a character is now how Papyrus is, for example). All of the songs are remixed to swapped characters as well.

Character Changes

These are the character changes of the canon Underswap like it was originally intended to be:

  • Sans is swapped with Papyrus.
  • Frisk is swapped with Chara.
  • Toriel is swapped with Asgore.
  • Alphys is swapped with Undyne.
  • Mettaton is swapped with Napstablook.
  • Flowey is swapped with Temmie. Friendliness Pellets and Tem Flakes are also swapped.
  • Asriel is swapped with Monster Kid.
  • Grillby is swapped with Muffet.
  • Mad Dummy is swapped with the Ruins Dummy.
  • Burgerpants is swapped with Nice Cream Guy.
  • Bratty and Catty are swapped with RG 01 and 02.
  • Onionsan is swapped with the bird that carries you over a disproportionately small gap.
  • Aaron is swapped with Shyren.
  • W. D. Gaster is swapped with the River Person.
  • Heats Flamesman is possibly swapped with Muffet's pet, though it's not certain if it was meant seriously or as a joke.


The protagonist of the AU, and the 8th fallen human.


A stuffed animal with Monster Kid's dust Undyne experimented on.


As former king of the underground, he turned his back on his wife to flee to the ruins where he welcomes fallen humans with open arms, caring and trustworthy. He offers you a nice cup of tea instead of a pie.


A small shy ghost in the outskirts of waterfall, dreams about being a TV star someday. Writes romance stories, and would love to share their collection of them with you. He's not pink, a misunderstanding created by the original image's pink-ish color.


Excitable and loving, training to become a royal guard with Alphys. However, as Sans and Papyrus keep their original stats, his low stats prevent him from being accepted. He enjoys making taco’s for his friends. His signature laugh is “MWEH HEH HEH”, he says "WOWZERS", and calls himself supreme and magnificent.


A laid back jokester who is into practical jokes, though shares a wide variety of other ones with Asgore. Enjoys honey as his favourite condiment and sells corn dogs as a side job. KR still is Sans' thing, and instead he has smarter and stronger attacks, though he is the one who is aware of resets and bleeds after his genocide battle. He wears hoodies with indirect posts on them.


Has a maid cafe in Snowdin town, confident and maybe a little smug. She sells croissants, tea and donuts, uses roller-skates to serve them to people.


Nice and friendly, sells burgers at his portable burger stand. The wrappers have a handwritten compliment on them.


Captain of the royal guard, fierce and unforgiving. Still enjoys her anime and helps Sans with his cooking every now and then. Instead of spear bullets she uses rotating axes. During the genocide route, she turns into "Alpha Alphys".

Ruins Dummy

Ruins Dummy fights Chara out of boredom instead of anger.


Wacky Flowers living in a hidden village.


Royal scientist, reserved and goofy, made Napstaton’s body for him. Enjoys watching anime/cartoons with Alphys. She thinks Mew Mew Kissy Cutie 2 is better than the original, but just like Alphys in Undertale, she knows that anime is not real.


The most famous radio DJ of the underground, charismatic and masculine (and frankly kind of a dingle). Calls people “bro" and "broski” instead of darling. He likes his arms just like Mettaton likes his legs, and has retractable turntables. He uses rhythm based attacks.


Protector of flames in all the underground. He sells fire based food to raise money for the flames in the Ruins. He's wacky and demanding.

Nice Cream Guy

Cynical and shabby, wanted to be a DJ but came to work in the fast food corner of the NTT hotel. He hates his boss.


Queen of the underground, ruthless and persistent. She can’t forgive herself for the lives she took from innocent children. She's more ruthless and emotionless than Undertale Asgore, and uses a scepter as weapon. She offers pie instead of tea.

Monster Kid

Asgore's and Toriel's adopted son, who died on the surface when trying to free monsterkind.


Frisk was the first fallen human, who poisoned themself to free the monsters.


  • At first, Papyrus was going to drink mayonnaise instead of Ketchup, but they thought honey would fit Muffet’s better.
  • The original idea of Underswap was never a full personality swap, though Frisk/Chara, Flowey/Temmie and Burgerpants/Nice Cream Guy do fully swap personalities.
  • It's stated Muffet’s is overpriced instead of Grillby’s selling points, but later on it's stated Grillby's is the overprized one.
  • Papyrus and Sans swap their use of upper and lower case, but not their fonts, obviously.
  • Originally, Undyne was supposed to love cartoons instead of anime, though it was later changed.
  • Originally, B&C where supposed to just swap clothes, but it was scrapped due to not making sense.