Incomplete~Killer!Sans x Fearless!Reader

Thinking, Dress Up, Masks

Are my friends really my 'friends'?
    What if they're trying to use me?
    They seem nice enough....
    Yet, you're still a hostage.
    I said let me think.
    Sure, sure. Just no gross stuff like love and crushes and shit.
   What? No! It's nothing like that!
   I could feel my face heat up like that of a cartoon character.
    Your funeral.
   Go away, stop putting these thoughts into my head if you don't want to see them.
     Sure, sure, whatever.
    Buuut, I suggest you wake up. Someone's moving you're bag around.
   "Wait what?"
    The room around shuffled and bent. I practically leapt out of my pillow fort. Being somewhat angry at whoever was touching my things, maybe because I was inside. I climbed up the ladder leading to the bags opening, and shoved my hands through, pawing at the face of that person.
     "What the fud-
     Before they could finish their profanity, I pawed their mouth.
     Unexpectedly, a fleshed face and mouth.
     Must be a stranger.
     "Put my living space down." I said, monotonically.
     The bag went gently back down to the floor, but kinda roughly, and I almost fell off the ladder.
     "Hey! That's destruction of property!" I said.
     Thankfully, the backpack didn't hurl me out, and I clambered up and out.
     Ungracefully, may I add.
     I look up to see whoever was messing with my stuff.
     "Oh. You're not Killer."
     "What the heck? Oh! Hello!" The girl said, drawing out the 'o'. She offered me a hand. I took it, and she helped me up. I studied her features. American voice, but somewhat Asian features. She wore a black jacket, with stitches hemming the middle of both arms and torso. A brown eye, the other one hidden by hair. Her shins went ever so slightly back, giving the slight impression of legs of an animal. Her hair was wavy and cut to her shoulders, and a pair of curled horn protruded from the sides of her head. She had the light eye bags of someone who had difficulty sleeping.
    "I'm really sorry, I wasn't going to snoop through your things, cool inventory though. I was just checking the house for you." She said. I smiled at her. Even though I just met her, it's as if I've always known her. "Sooo, what do you need me for?" I ask. She handed me a note, "Nightmare Gang wanted me to give this to you. They're mad." She said. How vague. I open the note, and read.
     Left for party. Get your ass over here. Or not. Either ways fine.
-NM-
     "Oooh shiiiiiiit." I mumble. I was so late. If I didnt get there within five minutes I was screwed. I didn't want to walk in when the party already started. It would be awkward. Asie sensed my worry, and laid a hand on my shoulder. "I'll help." She said, with a mischievous smile.
Ten seconds later...
"Get the costume on! When you're ready, I'll do you're hair. Oh wait, do you like simple styles, or fancy?" She asked. "Uh, >insert simple or fancy here< please." She nodded, and threw my shopping bag at my face, rather aggressively. She and Undyne would've gotten along well. I caught it, and went to the bathroom, tripping into the dress (or suit... I like suits.) and shoes. I came out of the bathroom, and the girl gave me a look over. "Nice, love the dress. Okay! Get back in there and sit down on that barstool!"
    "But there's no barstool...?" I say.
    "There is now!"
    An expression came to her, which was what I would call a game face. Concentration. Suddenly, shadows from the entire bathroom compressed in a single spot, and created a barstool in front of the mirror. That looked so cool. She smiled, obviously proud. I sat down, and felt the seat. The shadows where cool, and their texture like a very solid piece of jell-o, though, they didn't bounce around like jell-o. Weird but cool. I sat down, and she went to work on a >insert simple or fancy here< hairstyle.
About thirty seconds later...
I looked into the mirror, and somehow, she had managed to do my makeup while doing my hair. I hadn't even seen her lift anything to my face. "How did you do that?" I ask. She gave a smug expression, "Magic." She said, wiggling her fingers. Of course. She pushed me lightly off the stool  and asked me out of the bathroom. I obliged, and waited. About ten seconds later, she wore a jet black hooded cape, beneath an iron breastplate which had a type of delta rune etched onto the surface. Iron shoulder and shin guards, and a belt holding two daggers, and was brobably wearing one of those full body tights or whatever, which was dark, dark, purple. She smiled, when noticing my mystified expression, "I will not be attending the dance, since I'm one of the Patrolling Guards.  I'm also one of the guards who's supposed to take turns watching you're friends." She said.
     She looked legit, man.
     She looked around, and found a clock. "It's been five minutes. Golly, Killer must be flipping his lid." She said, darkly chuckling. "Okay, let's get you to you're 'killer' boyfriend." She said, matter o' factly. My face heat up at the usage of boyfriend. "He's not-
     "Shh. You two ought to be, since ya both have the feels for each other."
     "But I-
     "Cmon, we've a ball to get to."
      With that, she turned off the lights, and after a minute, there was a darker portion of the room, where shadows where thicker. She looked at me, "Now, whatever you do, don't stop breathing, or you may be lost within the shadow realm. It'd take me ages to find you and pull you out." She said. Okie doki. This sounds like a thing to check off the bucket list.
     She grabbed my hand, very tightly. "Let go, and you could be a victim of shadow creatures. Killer would make horror eat my face if I lost you." She said, very serious. I held on, and she and I slipped into the shadows.
      The shadow realm was a place of complete darkness. Everything was still.
Breath in. Breath out.
     Yet everything moved. Once, a creature that looked like a twilight zone fish, eerily floated past us, leaving a trail of black, dusty shadows. Creepy.
Breath in. Breath out.
     Suddenly, we where out. The light hurt my eyes a little, even though we where underground. Standing before a castle, which I assumed where the ball would be, I  looked around.
     I was observing my surroundings, when I was tackled to the floor.
     I stared up at the face of my attacker, only to see a mask.
     Held at spear point is somehow less comforting than knifepoint.