1 - 20 of 366 Works in Big Brother Sans (Undertale)
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You’re young. You marry the wrong man.
You wish you were dead.
Be careful what you wish for, Seven.
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Or, you find yourself Underground surrounded by starving, tortured monsters who know you're the last soul needed to attempt to break the barrier again. You said you wanted to die. Don't back down now.
Series
- Part 8 of How To Be A Human Being
- Part 9 of I/Me/Myself
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A FINE LINE BETWEEN ORANGE AND YELLOW by MairwynCSulien1990
Fandoms: Undertale (Video Game), Original Work
07 Nov 2025
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Summary
While Aneira didn't necessarily believe monsters existed, she did find the fact that everyone and their dog still did might mean something. Her childhood town of Beddgelert believed in monsters trapped under the mountains near their home that would need a seventh soul now to break out and destroy lands.
Aneira also knew that she needed to figure out what happened to the kid she was friends with who went missing. Which was how she found herself having fallen (probably) hundreds of meters below a mountain inside a cave system. Was she stupid for leaving without telling people where she was going, definitely, but, to be fair, she didn't expect to fall; she couldn't even see the hole.
Injured and wanting to go home, Aneira braves through the underground cave systems, finding MONSTERS both friendly and foes, learning about what happened to all the previous (children) HUMANS that fell.
tldr: Aneira falls instead of Frisk, is injured and is too stubborn not to use this chance to find out what happened to a friend (definitely dead by now, but she still wants to confirm), the Undertale cast feels like something is different, but not what. They also live in Wales here because why not?
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A Jaded Emerald by KTamao205
Fandoms: Harry Potter - J. K. Rowling, Undertale (Video Game)
06 Nov 2025
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Summary
Abandoned on Mt. Ebott at the tender age of five, young Harry's unsurprisingly died, but Death's always had a weird relationship with his variant... Meanwhile, before Flowey's revival as souless talking flower, Sans makes a discovery under the mound of snow, Papyrus has always wanted to be a big brother anyways.
*Edited Summary (29/09/2025)
Series
- Part 1 of MultiTaleVerse
- Part 1 of Arcalith
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I’m safe here (I’ll wait for a brighter day) by Ultimate_Sugar
Fandoms: Undertale (Video Game)
05 Nov 2025
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Summary
Gaster introduces his littlest son to a brand new game they can play, just the two of them.
This can only go well, of course.
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THE GREAT PAPYRUS PROBABLY DOESN'T NEED FOOD!
...probably being the keyword there.
But it's an experiment! A very scientific, very important experiment! And it has absolutely nothing to do with how disgusted food makes him feel!
Sans can't know about it. It's not that he doesn't trust him, no. It's just that Papyrus knows Sans wouldn't like the idea of his brother trying not to eat for a whole month.
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Eating never came easy for Papyrus. The taste, the texture, the strange disgust that followed... none of it made sense. But when he hears skeletons might not need food at all, something inside him clicks.
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In an experimental run, Flowey was worried Toriel would convince a fallen human to stay with her in the Ruins. Flowey was struggling to find a way to prevent this.
Luckily, a very “agreeable” skeleton friend of his might be able to convince her, but they’d need to target her kind nature somehow.
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Papyrus suddenly disappears. He’s in the Ruins with Toriel (due to unfortunate circumstances), but his other friends don’t know that.
Takes place pre-pacifist route!
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He was a bad brother. He knew that. He didn’t need all of this shit to happen for him to acknowledge that.
...Whatever it is that’s happening at this point.
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Papyrus made a stupid mistake and now sans is gone.
[THIS WILL BE REMADE]
Series
- Part 1 of MeryFell
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Summary
Papyrus hadn't been worried! ...Well. Maybe he had been, just a bit.
It'd been a while since anyone had heard from the human, so he called to check on them. But when a conversation revealed just how young they were, he realized things had to change. They were all on their own down here. And... They had nowhere to go.
Well! If there was no one else to take care of the baby bones, Papyrus would just have to do it himself!
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Sans was trying to get through life and ignore the apathy that had settled over him for Papyrus’s sake. It was just so hard to care about anything when he knew none of it mattered. But when Papyrus had him bring the anomaly home like a lost puppy, things stopped adding up.
How could such a sweet kid be responsible for the relentless time loops?
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Frisk was used to being on their own, and they were pretty good at taking care of themself. But—Well. ...Dying hurt. They just wanted to get back to the surface! With Undyne in the way, they were hopeless.
So when a phone call from Papyrus somehow ended with an offer for them to crash at his house, Frisk could only be relieved for the break.
They could afford to rest for a while, right?
Series
- Part 4 of Finding Home
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Summary
Who knew not knocking could lead to you knocking his socks off?
While at school, your friend Papyrus asks a favor, which somehow turns into you taking Sans's virginity :0
Porn with Plot
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Papyrus attends college and you are his Human Tutor by Spectascopes
Fandoms: Undertale (Video Game)
22 Sep 2025
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Summary
Papyrus, now a surface-dweller, decides he's going to go to college to meet human college students and become wildly popular. Being the first monster student at a human post-secondary school inevitably comes with a unique set of social challenges, but Papyrus is nothing if not capable! With the help of a new human tutor and his family cheering him on, he will acquire every degree possible and then some.
You are a part-time student who gets asked to help out the new skeleton monster you've heard screaming in the halls, and you couldn't say 'yes' fast enough.
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Papyrus was ten years old and had a head full of hopes.
Like every Tuesday, Sans worked at the lab with that weird doctor. And like every Tuesday, Sans was too busy to pick him up from school. This time, his brother also forgot to unlock the door before he left, which meant Papyrus would have to wait for his return to go home. Papyrus didn’t like the doctor. Month after month, he stole his brother a little more.
Who could have predicted that this ordinary afternoon would change his life forever?
When suddenly, a white dog.
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Month of Monsters 2025 Writing Challenge by SilvermistAnimeLover
Fandoms: Undertale (Video Game)
16 Sep 2025
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A collection of oneshots and shorts based off one-worded prompts from the September Month of Monsters Writing Challenge from my Discord server. Prompts will be listed in the first chapter, and they range from fluff to angst. Feel free to check out the first chapter (directory) to see what each prompt is about!
Fair warning, most will probably be Sans or Frisk centric.
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Adults lied. It was what they did.
They said they would take care of you, but they didn’t. They said they would be there, but then they died. Sans had gotten used to it.
But Papyrus shouldn't have to.
And if Sans had to take matters into his own hands in order to make sure he kept his promise to his little brother? Then so be it. It was Sans and Papyrus against the world, and some gangly skeleton with gentle sockets and a weird font wasn’t going to be the one to change that.
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“Sans, wait—! Please, let’s just talk for a moment—!”
“no way, you creep! leave me alone!”
“Excuse me? I’m not a creep! I just wish to talk! You have many people very worried about you—”
“nah, you’re not excused. gimme 500 g and then i’ll consider it.”
Series
- Part 1 of Finding Home
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Another Child Lost to the Mountain (Building a New Future, With You By My Side) by LizaVet
Fandoms: Undertale (Video Game)
15 Sep 2025
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Summary
Frisk could feel Chara narrowing their eyes at them. "Seriously, can you please take that stupid bandanna off your head?" Chara sneered. "It makes you look ridicul-"
"Mandanna," Frisk interrupted.
“…excuse me?”
"Mandanna. Not bandana."
”Are we seriously gendering the bandanna just because it has abs on it?”
"Yup!"
”…I really wish that others were able to hear your sass.”
"I don’t know, I kinda like the idea that you’re the only one getting to see this side of me." Frisk looked in the window of a house they were passing by, winking at their reflection in it. "Makes you special, doesn’t it?"
”I- Stop flirting with me. I’m a dead person’s voice in your head!”
"No."
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A child falls into the Underground and discovers a world beyond their imagination. Between the monsters, the magic, and the power to undo their mistakes and make everything right, they find happiness in places they would have never imagined. But when things start to get difficult, will they have the strength they need to keep fighting? How much pain are they willing to suffer to make things right? How much are they willing to give up to reach their happy ending?Series
- Part 1 of ACLM
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I like the head cannon of Sans having raised Papyrus. I also like the head cannon that all other skeletons died when the Barrier went up. So we all know PTA Sans, the punning and protective skeleton who join the PTA for Frisk. The thing is, in what I've seen, he acts experienced.So I like to think that he did the PTA before, for Papyrus. He had to make skeleton needs and growth and customs known to monsters who had never even seen a skeleton before. And we know how much Sans loves his brother, so he was probably very dedicated. Maybe he transferred some of that dedication to the human PTA.
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Papyrus knew something was wrong with his brother—people didn't drop their HP Cap for good reasons, after all. But last he'd checked it was much higher than ONE. With terror in his marrow and his brother staying stubbornly silent about whatever was going on, Papyrus decided it was time to call in the cavalry, because he would be damned if he stood back and watched his brother Fall Down and Dust without doing anything.
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Papyrus realizes that being on the Surface hasn't helped his brother's crippling depression, because his HP is still 1. So he decides to bring the others in on his brother's stats to try to help.
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The nightmare gets into Au without its powers. Even the author doesn't know what will happen.
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Sans turned to Papyrus. "you..sure you want to do this Pap? We can always send them with Undyne and Alphys-"
"YES, OF COURSE! FRISK IS MY FRIEND AND WILL NEED TO BE LOOKED AFTER IN THEIR SICKLY CONDITION. I AM THEIR BIG BROTHER AFTER ALL, IT'S MY DUTY TO PROTECT!" Papyrus frowns as Sans glances away. "YOU..DONT THINK I CAN DO IT?"
Sans' eye sockets widened. "no that's not it, bro. It's just..."
"Just..what?"
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Papyrus wants to prove he can be a good big brother to Frisk! How hard can it be to take care of a 5 year old human?
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“it’s just…you keep acting like something horrible is waiting for you at the bottom of this mountain.” His whispered voice was calculated and obnoxiously observant.
Frisk chewed their lip and felt their nails subconsciously start digging into their palm. The last thing they wanted to do was ruin anyone’s excitement about the surface with their own anxieties. If anything, they thought they’d been hiding their fears pretty damn well.
“There are some things, Sans…” their voice seemed to start against their will, hushed and constricted. They put a hand over their heart, which was beating restlessly.
“…that I just can’t explain to you,” Frisk finished exasperatedly.
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Summary
Frisk absorbs Sans' soul after an unintentional genocide run. In her grief, she resets to try to fix it and make everything right. However, things don't go as planned and she ends up in a violent version of the Underground. With Sans stuck in her head, she now has his magic to help them survive and escape. But Frisk is committed to sparing. It will be difficult to spare when everyone here wants to kill her. What will she and Sans do?