Undertale AU's
194 stories
An Oath of Mercy || UnderFell Sans x Reader by StrawberryMilkSnake
StrawberryMilkSnake
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One clumsy moment and a broken leg are all it takes to leave you at the mercy of the very edgy and very hostile monsters of the underground. Thanks to your knowledge as a doctor (and oath to do no harm), you're able to convince the Great and Terrible Papyrus to keep you alive. But how are you going to find your way back to the surface with a bum leg and a short skeleton that doesn't seem to like you? | - UnderFell Sans x Human Reader - Enemies to lovers but Fell is the only one hating - Your leg privileges are revoked, and Fell needs to wash his mouth with soap - Flowey is an equippable companion and decides to help you cuz he actually gets something out of it - My own interpretation of UnderFell (tho from what I've seen it doesn't really have a narrative anyway)
Universal Surface Angel  by Lithriel
Lithriel
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Reader insert. What if W.D Gaster didn't just get split between time and space, but actually ended up in your world in an abandoned hospital you called home? Your were a young child he decided to use as experiments to test human determination in said world and breaks physical laws to test human possibility? He knows of the powers you gained from his experiments... all but one, this one allows you to tear realities just enough to teleport into them. Knowing of Undertale you felt bad for the monsters stuck below in their world and wish to help them, but something goes wrong and you end up going to certain AUs and helping them, gaining the attention of some bad skeletons who now desire your power for them-selfish-selfs.
Forget Me Not (Dt Sans X Reader) by MegaphoneDouche
MegaphoneDouche
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It wasn't your fault you were in this situation. It just happened at random chance, now you were stuck in a loop. A endless repetitive loop of death and obsessive love. He wanted to keep you forever, and if it meant becoming a monster worse than anything, he'd be okay with it. After all, he LOVED you~ Heyyyyy Something I came up with, don't know if ill be doing smut with it or not, buuut hey, it's DT Sans, people seem to like him, updates will be slow, but please be patient!! :P Besides I don't think there's enough love for DT. Lol no regrets writing this whatsoever since DT Sans is bae for me ;) (June 5th: Lies, I have a new bae now ;-; and it's Horror Sans) Btw if gore and such makes you uncomfortable, I'm sorry my dude, but that's whats gonna be in this book. And some heavy angst between you the reader and Sans of course.. But of course budding romance!!! (I think..?) Verrrrry verrrrryyyy slow burn Tags will be added along the way
Furtastic by Juniperlives43
Juniperlives43
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A girl who has never seen the world outside of the lab sees it for the first time only to fall down into the underground. What will she find down there?
- My Angel from the Sky - Gaster x Reader by MonicaGiudice
MonicaGiudice
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Suddenly you find yourself in the Underground, with no memories and an unknown and painful past. Your first encounter is Flowey and he tells you how weird and different your soul is. What does it mean ? What happened to you ? A fated meeting awaits you. The beginning of everything. THE UNDERTALE P.S (GasterxReader) The beginning of the story is set some years after the war between humans and monsters. #9theories 9/05/2018 <3 Thank you guys :D #8theories 10/05/2018 <3 #1 gasterxreader 16/08/2018 <3
Are You Loyal? [Lust!Sans x Reader] by Fandomz_Fanboy
Fandomz_Fanboy
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Your boyfriend was just caught cheating on you. You got mad at him for buying a prostitute and fucking her, so he threw you out. To compensate with this loss of the guy who stole your precious virginity you go to Grillby's. You didn't expect a certain Pole Dancer to catch your eye. Disclaimer: UnderLust doesn't belong to me Warning: Lots of vulgar language and lewd topics.
Endless possibilities (Underfell Sans x Gender Neutral Reader)*BEING REWRITTEN!* by glossedweed
glossedweed
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Word has been released that monsters now roamed the surface, and you can't help but feel slightly skeptical. You had been told since childhood that monsters were vile and repulsive creatures who wanted nothing more but human blood pouring from the palm of their hand. You didn't know what to think of the monster race, but majority of the human race did. The tension between monsters and human kind was sickening. People had told you to stay away from monsters at all costs. But that'll be a bit difficult when two skeleton brothers move in next door to you. And why bother lying? You can't deny that one of them has stuck on your mind. (Warning. There's a lot of colourful language, so just a heads up. And also, the artwork doesn't belong to me. Credits to the rightful owner.)
Scientist - GASTER X READER by NapstabIooker
NapstabIooker
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Hi guys! So this is actually my first time writing a adventure story (and xReader), so I am kind of sorry if it looks crappy!! ****** A long time ago, people were missing when they climb up Mount Ebott. They say there was magic, got lost, or even died. But when you discover the secrets of the mountain, you will get attached to it, and even maybe meet a new 'friend'... ||an W.D. Gaster x Reader fanfic|| •I do NOT own any type of artwork that is included here in the fanfic, all art goes to thier respective owners.•
The One Thing That They Care About (Sans AU x Reader x Papyrus AU) by voltimer
voltimer
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Y/n L/n. A special human with a special SOUL. Yes, her Soul Trait is something new. But other than her SOUL trait she has another secret. One day, while she was at the surface with Frisk and Sans. 6 skeletons appeared out of nowhere, making raging screams and chaos as maniac laughter filled the air in their wake. Soon they found Classic Sans with Y/n & Frisk. But when they saw Y/n, they were curious of how she can wield magic powers and be brave. Soon they took Y/N with them, to their castle. Will Y/n tame them? Or will Y/n fail and suffer the consequences? Involving a Bad Sanses x Reader x Star Sanses plot. Along with various Alternate Sanses. #1 in badsanses at 17/01/2021 #1 in ausanses at 31/01/2021 #2 (Out of 21.8K) in nightmare at 24/02/2021 #38 (Out of 48.1K) in undertale at 21/05/2021 #3 in (Out of 3.42k) Cross at 18/12/2021 #1 in Dust (Out if 2.15k) at 18/12/2021
Void [Nightmare X Reader] by LotusdeCeniza
LotusdeCeniza
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Y/N is the Guardian of nothingness. The shrub with flowers that she protects is home to all things that are considered to be nothing. When a walk in the woods allows her to make a new friend,a problem arises from the shadows. As Y/N tries to find balance between the protecting her plant and Nightmare a margin of error disrupts peace between feelings. Destruction and despair have plaguaged her once beautiful home because of this. How will Y/n help revert things to how they once were before. Slow burnish, on going nightmare x reader Not edited, cause most of this is written on the fly. Update monthly cause uninspired and school. Highest rankings: #1 dreamtale #1 Negativity #1 nightmarex reader #1 Sansxreader #1 nothing #1 passive #1 balance #1 Nightmare #1sans