Best Sans/Reader Slow Burn Fanfics

by this_is_my_alt

A misunderstanding lands you in a meeting of monsters and fetishists. From the chaos you find yourself in the dynamic company of a kinky Mutt, gasterblaster! Sans, and a cat-ear wearing Axe.Deals are made. Boundaries are broken. You become thoroughly entangled in this group of horny skeletons with v

by MissSugarPink

Your name is unimportant. Your job is nonexistent, really. And your (ex)roommate just kicked you out in the middle of a surprisingly cold November night. But whatever. You don't care. You'll be fine. Keep telling yourself that as you freeze to death, idiot. But you'll be fine, for one reason! Two, a

by absurdmagewrites

Sometimes life throws you a curveball. For you, your curveball was going to bed looking like a human, and waking up looking like a monster. A skeleton monster to be precise. With the barrier breaking, a large surge of magic descended on the town you live in, and transformed you overnight. Unsure wha

by Or13M

When the quiet solitude of your new life is disrupted by a gaggle of skeletons moving in next door, you and your sibling find yourselves pulled into their orbit. Healing takes time, but maybe, this chaotic, affectionate family is exactly what your soul has been waiting for. *Inspiration taken from "

by Quinme

One moment you were on the call with your friend, the next you are in a shady dark alley, pressed by... a crocodile in fedora? Life is confusing, and you have no damn idea where you even are and what will come next.

by charamelwrites

You were kidnapped by the Bad Sanses gang because you apparently "stole" Horror's axe. All hell breaks loose. arc 1 (1-15): encounter arc 2 (16-?): after

by Asaila

You only wanted a normal life. Then you met them. Sanses and Papyruses from different worlds, each carrying their own past, their own wounds, and their own ways of becoming part of your life. For a while, it almost felt simple. Then the timeline broke. Now everything has started over. They don’t rem

by Mayumara

You were an ordinary maintenance worker, part of the crew of the Aurora when it crash-landed on an alien world and left you stranded in a hostile ocean. There are probably worse places to be stuck; at least the scenery is pretty, and you've always been passionate about marine life and alien research

by KittyCatPaw11

There are a number of little ideas within my head—or strikes of inspiration from fellow Undertale creators—that I'd love to write about! But they need a home... Welcome to Reader x Everyone in the Multiverse! I don't have a schedule, but I try to post often! I hope you enjoy these stories :3c

by B3_l

[Honestly.. After everything you've been through you didn't expect to find yourself here, in the middle of a fight between two men you recognized too much to be normal, with your unconscious husband in your arms having a near death grip on both newborns while you could at least stand without feeling

by FuCkInG_FaBuLoUs

Hmm, such a thing of wonder in this crowdI'm a stranger in this townYou're free with meAnd our eyes locked in downcast loveI sit here proudEven now you're undressed in your dreams with me ~~~~~~~ You didn't cheat out of retaliation. To make things even. Perhaps some part of you did, a small vindicti

by Strawberry_Milk_Snake

There's only one rule for those capable of AU hopping: never bring a real person into the Undertale multiverse. But, like all rules, it was destined to be broken.

by pessimistic_frog

Most people spend their whole lives wishing that someone would come along and sweep them off their feet. But what happens when that person is already in a relationship? Who will fate honor? And who will be cast aside in the dust. And the more important question... who will get a better grade on thei

by Puppy_Chat

Y/N's life in the village is changed forever when a new monster enters her life... Soon everything starts changing and coming to light... The only problem is.... Everyone knows, but her....   (Summary Updated on May 28, 2026)

by AleonaIceCream

You recently moved into this mansion, and a few days after getting all the stuff over, you have a thirst for waffles, but you don’t have sugar at home! Unable to wait, you walk to the neighboring mansion a couple minutes away, and find some things (more like a couple someones) that shake up your new

by WillowSparrow

Your best friend Sophia has been going on and on about this stupid romance game featuring skeletons and yanderes. You thought it was stupid. Well, until you were literally transported into it, but not as the protagonist. As the villainess.

by Housanweiaaa

No summary provided.

by pessimistic_frog

Roman is your average college student. Overworked and underfucked. Too little sleep and too much caffeine. However, she starts to find that her serious lack of sleep is leading to some crazy dreams. Dreams in which she's now a skeleton, with three alternates, and a buncha other skeletons that seem h

by Kustal4life

You've accidentally brought your alternate into this world, + Classic AU versions of Sans crash into his universe, but the completely unrelated machine is broke and they need to get home. The how will they all do it? Tune in to find out eventually.

by Andrea777Cats

No summary provided.