Undertale AU Sibling Oneshots

Dreamtale! Bros x Adopted! Reader

Requested by the lovely corvid, @YourNekoNekoKneecaps!~

(Grade A username right there. I love it.)

"...N-Nightmare...?" Your voice came out shaky, watching the dark tar-like substance spill from your brother's mouth.
A deep, angry growl followed your tentative call, Nightmare turning to glare at you.
It had been like any other day, you wandering through town with your brothers, chatting about nothing in particular with them as you gazed around. The townsfolk were setting up for some sort of festival, which would be happening later that evening.
You were excited, Dream sharing the joy with you before dragging you off in some direction. You were oblivious as Dream snatched you away, leaving Nightmare to either follow or get left behind.
Seeing what Nightmare had resorted to made you realize just how often Dream pulled you away from him.
Perhaps he didn't mean to do it so much, but now wasn't the time to ponder over that.
"Nightmare...?" You called again, daring to take a few steps forward, even as your instincts told you the opposite.
"Get back, (Y/n)." Nightmare spat, droplets of tar flying forward, staining the grass between you. "Just stay out of the way, I have something to settle with Dream."
"Nightmare, you don't have to do this..."
Nightmare shook his head at you, clearly struggling to stay himself. "You don't get it. Dream always dragged you away from me. It's about time he gets what he deserves."
"But—"
"Enough."
Nightmare pushed himself to his feet, another bout of tar dripping down onto the grass. You sprung forward at the sight of a wince from him, wrapping your arms around his middle, the tar beginning to cover him now.
You felt him pat you on the head, a dark chuckled echoing from him before he pushed you from him. It was a bit harsh, but granted what he looked like now, you could only assume that was his gentle.
A dark, evil grin and one glowing blue eye turned to you. "Where's Dream, (Y/n)?" (There's Something Happening by Jack Stauber just came on when I got to this point... fitting)
"I'm right here, Nightmare."
You weren't sure if Nightmare's grin could get wider as he turned to see Dream standing there.
"Please don't!" You were quick to grab Nightmare's arm, trying your hardest not to cringe at the sticky, cold tar that seeped past your fingers.
"And let him get away with keeping you from me? He's practically had you all to himself lately (Y/n)!"
"I'm sure he didn't mean to keep me from you!" You tried to reason with him, but once again you were pried off of your brother.
"He's the one that found you, (Y/n)." Nightmare continued, glaring at Dream now, "He tried to hide you from me, keep you all to himself."
You glanced over to Dream, tears forming at the guilt in his expression.
"Why...?"
"I've always been lesser than him." Nightmare hissed.
"Nightmare that's not—!"
A tendril shot out from Nightmare's back, swiping at Dream. "Quiet you."
"Nightmare—"
Another swipe.
You took a few steps back, unable to believe your brothers were fighting like this. Dream had tried to keep you from Nightmare...?
Why...?
Had he somehow known Nightmare would do this? Was it an attempt to keep you safe?
You whimpered and ducked your head, turning your gaze away from the fight as Dream got flung, landing with a harsh thud.
You weren't sure how long the fight lasted, but eventually you were scooped up by Nightmare, getting only a glimpse of a beaten up Dream before Nightmare whisked you away.