Undertale AU Sibling Scenarios

Horrortale Bros X Insane! Reader

This is what you look like (kinda), you can change up the colors a bit if you wish. Also, I made the eyes rainbow to symbolize any color you wish. ^^

You weren't exactly insane like your brothers, probably the only sane one in the underground. Yet there were many monsters who would love to see you snap. Which caused many monsters to harass and insult you, or spread rumors.  They often hit you hard with their words. Yet you ignored them the best you could. There was only one topic that would make you snap. Sans knew you were going to snap eventually, he dreaded the day.
Today you were cleaning your room since it had gotten messy and Papyrus asked you to clean it. Not wanting to make him upset, you decided to clean up.
You found a lot of stuff you had been looking for under your bed, one of your old sketchbooks, a picture book of you and your brothers, back when things weren't chaotic, some other random things - like a pair of headphones, and a...baseball bat? Your eyes furrowed when you pulled the object from under your bed. Shrugging, you placed the bat against the wall behind your door before continuing to clean and organize.
You walked downstairs to see Sans burst through the front door. He looked pissed.
"Y-you ok, Sans?" You timidly asked, to be honest he scared you when he was mad.
"Have you seen Papyrus?" He snapped. You shook your head.
"I was cleaning my room," you muttered "What happened?"
"Someone claimed they were gonna kill him." He snapped again. He started to turn and head back out the door before he froze at your sharp voice.
"Who?"
He turned to look at you, your eye lights were out, leaving black pits of anger and fear.
"Some rabbit named F-Fluffy, I think..." he muttered, dread filling him as he feared one of his worst nightmares was going to happen.
"I'll handle Fluffy, you go find Papyrus...I want both of you to stay at home until I get back tomorrow morning..." you growled. Even though you were the second eldest, Sans wasn't going to let his little siblings get hurt.
"(Y/n), your not gonna ki-"
In that instant you teleported in front of Sans, grabbing him by the collar of his shirt and pulled him down to your height.
"I can handle insults and death threats thrown towards me, but nobody, NOBODY, claims they are going to hurt my brothers and get away with it. Sorry Sans, I can't stay stable any longer..." you snarled before you muttered the last bit. Releasing him, you went upstairs to plan your night. You had a few friends who knew what exactly was said and who plans what. You like to nickname them your spies from time to time, which they didn't mind, they liked doing it for a living. And, the best part about them is that they didn't ask for anything in return.
After talking with them, it was proven that Fluffy did make a death threat towards not just Papyrus, but to Sans as well. You growled before seeing the baseball bat behind your door...

(Choice[both are different than the other, I tried doing more different endings than my other siblings scenarios])

Sans:
You asked your spies if they could bring Fluffy to the abandoned shed deep in the woods and have her tied up. After getting a picture from them of Fluffy tied up, showing they did their part, you grabbed your bat and made your way to the shed.
God you hated Fluffy, not only did she insult you and threaten you, she left you three cracks on your right eye socket.
Arriving at the shed, you opened the door and heard it creak open. You heard sniffling and slight panicking from inside. You let out a chuckle.
"W-who's there?!" Fluffy screamed. Her eyes were covered, but not her big mouth. Stepping forward, you closed the door behind you.
"Oh, just the sister of the brothers you made death threats to." You said nonchalantly, deciding when to strike.
"PFFT HAHAHA! You kidnapped me? How the hell did that happen?" She cackled.
"Oh I didn't kidnap you, my spies did."
"S-spies?"
"Uh-huh."
"What do you want with me?!"
"You're kidding, right? Pfft. Take a guess."
By now you were standing in front of her, staring at her.
"I...I-I dunno..." She eventually muttered. God is she this stupid? But that's what makes it fun, I guess.
You smiled wickedly as you sat there, listening to the silence. She grew more nervous and fidgeted more every passing second, muttering your name every now and then. Reaching forward, you pulled the cloth away from her eyes. Seeing your insane, dead expression, she started to scream until you clapped a hand over her mouth.
"If you want to live I suggest you stay quiet." You whispered. Fluffy freaked out and managed to get her leg loose of the ropes before kicking you in the face, worsening the cracks on your cheek. You placed your hand to that spot for a few moments as she struggled to get loose of the ropes. Your eyes snapped open before you lunged forward and busted the baseball bat across her knee, hearing both a satisfying crack and an ear piercing scream.
Smiling wickedly, you raised the bat above your head.
"No...nonononoNoNoNONONO!!!" She screamed before your bat made contact with her head. Her screams faded into nothing at the last two hits.
You looked down to see blood mixed in with the dust that spread across the chair and floor. Letting out a cackle, you left the shed and headed home in the dark of night.
Entering Snowdin, you saw someone standing under the porch light as you neared your house. Getting closer, you saw it was Sans when he looked up. When he saw you he jumped over the porch railing and ran to you, enveloping you in a tight hug.
"(Y/n)...what did you do?" He asked, leaning back and looking at your blood covered hands and face. A sickening grin spread across your face.
"I protected my family."
He sighed, before hugging you.
"Ya know, a part of me always wanted to see your crazy side." He whispered as he smiled. You hugged back and fell asleep after he picked you up and carried you inside.

Papyrus:
You had gone out in search of Fluffy, you had your bat with you, but you stayed in the shadows. You knew exactly how to draw Fluffy to you, you just had to get her to notice you.
Finding her leaving a shop, you got her attention and acted like you were avoiding her. Noticing her smirk, she made her way over to you. Turning a corner, you waited for her to follow before smacking her over to head.

You dragged her to an abandoned shed deep in Snowdin Forest, tied her up, and waited for her to awake.

When she awoke, she stared at you, then the ropes, and then back to you.
"Do you seriously want me to believe you did this? You're too stupid and weak to do this! Show me who's done this!" She exclaimed angrily. When you didn't move she laughed.
"So, I guess you did do this? Surprising, I figured after all the insults thrown at you you'd be too depressed to do anything! Did you hurt yourself while planning your revenge?" She sneered at you. Your eyes narrowed.
"You just listen to any insult and threat thrown at you, not seeming to care. Don't you have any self respect?" She continued to taunt you. Your anger boiled at this point.
"I bet...you can't even stand up for yourself. Probably always going to cry to your brothers. Not like I care, just go ahead and keep feeling miserable!"
"SHUT UP!" You screamed as you lunged forward and hit her in the shoulder, hearing it crack. Your face split into a horrid smile. You cackled and she screamed as you repeatedly hit her in the head. Seconds later, you were covered in blood and she was dust.
Turning around you stepped out into the forest, dust spreading into the air. You trudge through the dark, your bat dragging in the snow behind you, leaving a trail of blood and dust.
Halfway home, you saw someone running towards you.
"Pap?" You said aloud, recognizing the figure.
"(Y/N)!!!" He exclaimed, reaching you and pulling you off the ground in a hug.
"Paps?" You mumbled.
"ARE YOU ALRIGHT?!" He asked, holding you in front of him with ease.
"I'm fine Paps..." you muttered, looking away, feeling ashamed for making him worry. Hugging you again, he carried you home.
"Did...you snap?" He asked quietly.
"Nobody hurts you or Sans..." you muttered before falling asleep, cutely snuggling into his scarf. Papyrus smiled and held you closer.