You love cosplay, ya cant help it, your so obsessed with it that you have no normal clothes, its all cosplay. Growing up your parents never really approved. They thought it was strange and weird to want cosplay. They just couldn't understand. So they didn't let you become a part of that world. However they couldn't stop you once you moved out. And once you were free everything was cosplay. Eventually you started taking pictures of your cosplays and then you started taking the pictures in more exotic backgrounds. And thats when you found yourself on mount abbot with your trust backpack and camera and cosplays. And thus our story begins.

You find a cave that you deem perfect for a specific cosplay back ground, as you venture further into the cave it gets darker and then you trip and fall into the hole onto that bed of flowers. Flowey spots you, but your in cosplay which doesnt exactly make you look human, he avoids you. Toriel spots you, not recognizing you or realise ING your human drags you to the ruin door and tosses you out, you think she is also a cosplayers and this is a secret cosplay convention and she just didn't like your character, toriel walks away slamming the door behind her.  Sans sees you exit from that door he's never seen you before and you dont look human and you look sort of attractive. But he brushes this off. You look lost. You might be new in town so he decides to take it upon himself to make sure you know how things work here. He approaches, the closer the gets the more of you he sees and the more of you he likes. You are so obsessed with your cosplays that you always stick with the character that you are, no matter the circumstance, so when this skeleton monster approached you analyze his features which portray him in a seemingly strange skeleton cosplay, you can't help but admire how real it looks, your excited that so far everyone seems just as devoted to cosplay as you. You can't help but compliment him for his 'cosplay' you tell him he looks amazing before going back into character he blushes at this statement, which amazes you even further, but you continue to stay in character. He asks you if you're new around here and you nod. He tells you to follow him. You follow him. And then you see what appears to be another skeleton cosplayer, yelling at sans from a distance, sans tells him that you're new around here and Paps introduces himself, and you exchange questions, them to get to know you and you to understand their characters. apparently their characters are siblings and their both edgy. At a point in time Paps starts talking about his armor and how amazing it is and brags about how he made it, you cant help but say he is so cool after hearing this, considering the quality of his cosplay is amazing. Sans and Paps look at you like they've never heard a complement before. Sans is intrigued by you even more and Paps is astonished someone as kind as you exists, and lets out a cough of gratitude, you see this as him trying to stay in character. They ask if you have anywhere to stay, you dont so they offer to let you stay with them.as you make your way over to thier house you cant help but ogle over all of the amazing cosplays. Once you reach thier house they realize they only have two bedrooms, and Paps declares you'll share a room with sans! Your perfectly fine with it because your use to share ING a room with other people due to your group convention outings. Sans emotions seem to be conflicted between lust and awkwardness. Sans leads you to his room which reeks of mustard and depression. You set your stuff down on the floor and ask sans where in the room you should sleep, sans offers you the mattress and says he can sleep on the floor but you refuse and insist that he keeps the mattress. Sans says they might be able to find another one in waterfall, and you say that they could always deal with that later. You head back downstairs to see Paps and Undyne arguing about something (alphus seeing and anime character come through the ruins). Undyne spots you, and yells out, aha! I knew it! anime is real! Your a ___ right punk! You nod. Undyne yells out again, I knew it! Alphus you liar! Undyne screams storming off. Sans comes out of the room behind you and asks about the screaming, and what the f*ck that was about. You say it was about you being a ___. Oh so thats what you are, Hmm...sans thinks to himself. You still think this is all just really devoted cosplay. Oh you poor naive child. Sans asks you about the being a ___ thing. You answer how your character would answer. Eventually Undyne comes back. And demands that because your a ___ she wants you as her pet/personal guard. Alphas isn't happy bout this, neither is edge. Paps is the first to speak up about it. He says that sans was the first to discover the ___ therefore if she is anyone's pet she should be Sans's. You are kinda disturbed by the thought of being someone's pet, but what did you expect from a bunch of Edgey characters.  Sans blushes slightly, and you notice, and blush as well, now that you think about it, you rather be Sans's pet than anyone else's, he seems the least likely to do something horrible to you, so naive y/n. Then it's decided says Undyne, y/n will be Sans's pet! Sans is blushing more noticeably, and quickly hides his face, and reminds Undyne that you should decide whether or not your a pet or not. Unfortunately everyone but you ignores him, you think its cute that he tried to vouch for you, you try to voice your opinions but you are also ignored. You then feel something click around your neck. It's a collar. You look at the tag, it resembles a heart locket, inside is a glowing white upside down heart. You try to take it off but it doesn't work. Sans looks like he is about to say something, but papyrus interrupts him, and tells him to not make any attempts to take the collar off you. You look at him pleadingly, but he just shoots you an apologetic glance.

To maybe be continued..

~

The underground is a mess, everyone is Edgey as f*ck.
Skele Tongues are from a hormonal skeleton making a bad decision.
And mettaton getting involved.
How the collar thing works is they are locked via soul. So only those with the soul matching the lock can unlock it. The reason papyrus insisted for sans instead of himself is because each monster only has one. For soul related reasons. And he put one on sans.
Papyrus always overrules sans, always.
It would take a lot for sans to overrule his brother.