Undertale AU Sibling Oneshots

Nightmare x Male! Reader

(As requested, you are not biologically related to Nightmare, but ur still a skeleton!)
(*vibing to SharaX as I write*)
Requested by the lovely corvid, @ASunny1!~

You followed Nightmare through his castle, and you had to admit it was impressive. Naturally you followed Nightmare in his decision to cause chaos throughout the multiverse, knowing the pain everyone else at home caused him.
"And here's—"
You both flinched as a bone whirled past you, anger flashing in Nightmare's gaze as he whipped around to the group in the room.
"Are you all dumb?!"
You glanced into the room, seeing a group of equally-bad looking skeletons. They all shuffled nervously, avoiding Nightmare's gaze.
Nightnare sighed, pinching the bridge of his nose bone. "Here's the others. This is Fell, Horror, Dust, Error, Killer, and Cross."
They all waved in turn, and you waved back before chuckling. "You guys having a sparring match or what?"
"No!" Error hissed, sounding like static, "HoRrOr RaIdEd ThE fRiDgE aGaIn!"
"You know how I get!"
Nightmare rolled his eyes, grimacing in annoyance. "Let's just continue on, (Y/n)."

You'd been living with the bad team for a few weeks now, taking place as the gang's healer, which meant you got to boss them around a bit as you tended to their wounds.
"Will you hold still?! Or do you want me to leave this crack here to get worse?!"
Fell huffed at you, slumping back down in the chair you shoved him into, wincing as you worked on healing him. Your healing magic wasn't the best, but it was better than anything the others could attempt.
"Alright, you're good. Don't do anything dumb." You let Fell go, watching as he left the room, only for Nightmare and Cross to follow.
You sighed gently at their scuffed forms, gesturing silently for them to sit. You tended to Nightmare first, his firm taking to your healing quicker than the others.
"Alright you're good!" You chirped, refraining from patting him on the head like you did the others. He nodded his thanks to you, lingering in the room as you switched your attention to Cross.
Cross didn't huff or whine at you like the others, seeming more relaxed even, and so you decided to fill the silence with some small talk.
"So what all did you guys get into?"
"Fell had to go back to his AU for something and ran into his brother, Cross here had another fall-out with Classic and Ink, and of course I ran into my brother, Dream, again." Nightmare replied, growling at the mention of his brother Dream.
"Hope you two gave em all a beating, not fair you guys got treated so harshly with your AUs."
"You bet we did!" Cross piped up now, grinning up at you as you pulled away, your healing magic dissipating.
You offered a shy smile in return.
"Is there something going on between you too?!" Nightmare hissed, and your magic ran cold.
"Nope!" You and Cross yelped, taking each other's hand to run out of the room, laughing as Nightmare chased after you both for answers.

(*peeps out from under my rock* *gives you this and hides under my rock again*)
(Hi sorry I've been inactive.)