Undertale AU Sibling Oneshots

Abused! Fell! Sans x Sister! Reader

Requested by the lovely lostabandonedsoul!~

You had just about enough of it. Sans would come home with injuries that were getting increasingly harder to heal. Papyrus just wouldn't let up on him, despite you being worse at your job than Sans is at his.
You slipped into Sans' room one night, gently urging him awake in a way only you could do. Everyone else usually scares him awake, but you're the only to not scare him.
"Whazzup, (Y/n)?" He slurred, still half asleep.
You held your hand out to him. "Do you trust me? I have an idea of how to get you away from Papyrus."
Sans took your hand without hesitation, and you teleported you both off to Alphys' lab.
Alphys was waiting right where she said she would.
You immediately ran up to her, giving her a tight hug. "Oh thankyouthankyouthankyou! I definitely owe you one for this!"
"It'll end up as two if you don't stop hugging me."
You quickly let go.
"Alright," Alphys continued, "I've got the guest room set up for him, I'll see what I can find in terms of healing items."
"Thank you again, Alphys!"
You turned and began pulling Sans along to the guest room.
"I asked Alphys to let you stay here for your safety." You explained, "I can't stand seeing Papyrus hurt you anymore..."
Sans looked like he was about to cry.
"How did this f*cked up world not turn you into something like everyone else? How the hell are you so sweet, (Y/n)?"
You shrugged. "I dunno. I just know I gotta take care of my siblings even if they're older than me."
Sans shook his head at you, stepping forward to hug you tightly.
You hugged him back, eventually coaxing him to lay back down in bed to rest.

"So what are you going to do once Papyrus sees Sans isn't home?" Alphys asked you.
"I'm gonna act like I don't gotta clue."
"And if he sees through it."
"Pray I don't die a horrible death before I can get here."
Alphys shook her head lightly at you, poking you as she spoke your next words.
"If he does start hurting you. I want you to come straight here. Got it?"
"Got it." You have her a firm nod before teleporting back home.

For once in your life, you were "sleeping in", considering you could hear Papyrus fuming in Sans' room for the past 30 minutes.
You jumped when your door suddenly slammed open, and you were quick to fake looking like you'd just been woken up.
"(Y/n)!"
"Wh-What!?" You sat up, blinking tired eyes.
"Sans is missing."
You furrowed your bone brows, detangling yourself from your blankets. "Missing?"
"Yes! I wonder if the lazybones has finally ran off!"
Papyrus turned and stalked downstairs, and after getting dressed you followed him.
"A-Are you going out to look for him?"
"Of course I am! Check the forest first, I'll check around Snowdin."
"Okay..."
You trotted off into the forest, going the usual route you'd take when looking for Sans. You kept Alphys updated along the way.
She reported back that Sans was fine, and that he was healing better with her remedies and his ability to sleep more.
You wandered along the routes for a while, eventually stumbling on the path near the ruins.
"Did you find him!?"
You jumped at Papyrus' sudden appearance, and shook your head once you spotted him.
Papyrus began grumbling under his breath.
You stayed quiet, just like you usually did.
You never really spoke up against Papyrus, in fear that he'd start hurting you too. Seeing Sans hurt was bad enough, you wouldn't want to feel what he's going through and neither would he.
"I'm guessing he wasn't at Grillby's?"
"No! And Grillby hasn't seen him either! No one has since yesterday!" Papyrus barked. "When he gets home I'll—"
"You'll what? Hurt him some more!?"
The words left your mouth before you could stop them, but you just couldn't stay quiet anymore.
"Y'know maybe that's why he ran away! Maybe he's tired of you beatin' the sh*t outta him every day so he ran off!"
"(Y/n)..."
You glared up at him. "Oh yeah, I see the sh*t you pull everyday! You wanna know how Sans gets those injuries healed? Me! I'm the one that heals him everyday! I'm the one that's there when he needs to cry or vent!"
Papyrus' eyes flared up, but you were one step ahead of him.
"Try me! See what happens when you hurt me! Your ass will be cooked Papyrus!" You turned away from him once there was no sign of immediate attack. "Now if you'll excuse me, I'll be leaving."
You walked a few steps before teleporting, not risking the chance of Papyrus following you to Alphys'.
You took a deep, shuddering breath once you were in Alphys' lab, letting it out slowly to release your tension.
Slowly, you felt Sans' arms wrap around you.

You and Sans were in Waterfall, just enjoying each other's company as you talked about nonsense and absentmindedly made flower crowns together.
Sans was relaxed, and for once his eyelights were showing, and not the red glowing eye he always had.
But you watched as he glance off to the side, his carefree smile falling and that red eye returning as fear gripped him.
Already knowing without looking, you jumped to your feet and turned towards Papyrus, tense and ready for whatever he had.
He looked almost mad for a moment before a sharp tug on his scarf caused him to stumble and turn, a small human showing up behind him with a disapproving frown.
He murmured something in response, and then turned back to the both of you.
"Sans? (Y/n)? Can I talk to the two of you?"
You narrowed your eyes, but with Sans' permission, slowly stepped forward with him.
"What is it?"
"I wanted to apologize."
You both blinked, staring dumbfounded at him.
"My previous actions were inexcusable, and I want to make up for that by doing better."
"And..." Sans peeked out from behind you, "How'd you come to this relevation?"
"This human came from the ruins a few weeks ago and has taught me better."
The small child waved, the flower hiding behind them slightly.
Sans looked at you and you looked at him, silently going over Papyrus' offer.
After earning Sans' miniscule nod, you turned back to Papyrus.
"Fine, we'll accept your apology. But if you slipup, we're done! Got it?"
"Of course, (Y/n)."

Papyrus ended up keeping your promise. There were times he got mad whenever one of you genuinely messed up, but he would always take time to calm himself before confronting either of you.
After that, Frisk managed to get the monsters to the surface, and now you spend your days goofing off with your brothers, not having to worry anymore about patrols of Snowdin.