This is something I've been thinking about for a little while; I might do more of these if you really like it, but for now I hope you enjoy.
The Underground may not be the most welcoming of places, but at least the monsters who lived there considered it mostly safe. But monsters do get destroyed from time to time and when they do… a special person comes to visit them.
It was believed that when a monster dies they cannot be brought back because their body converts back into the raw energy that made it. Energy is replaceable, but the spirit is not, and when a monster dies its spirit is the missing piece that stops it from returning; not even all of the determination in the world could fill a hollow soul.
On this day Sans walked through the forest alone to try and clear his mind, he wanted to be as far away from his brother and all the other members of Snowdin as possible. Seeing them would only make things more… difficult for him. As he walked though he could feel something following him, something that made next to no sound but made the air around him cease blowing and made a chill run down his spine even though he didn't have any nerves.
He tried to ignore it at first, but the feeling seemed to get closer and he knew that he would have to acknowledge it eventually.
"if somebody's following me, can they please make themselves known?" He yelled to seemingly no one.
In that moment he felt it disappear, but when he turned around to continue his walk he saw a tall hooded figure in a black cloak appear before him. Sans was shocked that he just appeared before him, but he remembered that he was an odd duck himself and knew how to move quickly without explanation as well so he didn't question it.
"what's with the getup buddy? you look really… cloak and dagger." Sans joked
The figure didn't make a noise but his shoulders moved like he was trying to hold back a chuckle.
"Very clever Sans."
What Sans had learned from this conversation so far was that this figure had a voice as soft as a whisper but the words carried like a trumpet, and it sounded like this person's throat was dry and dusty. The second thing Sans noticed was that this person somehow knew who he was.
"heh, you got me at a disadvantage stranger, you know who I am but I got no idea who you are."
The figure kneeled down. "Oh come now Sans, even if you've never seen me before you've most certainly heard of me. In fact… you know me very well."
The figure began to remove its hood and the second it did Sans' eyes went wide, the figure behind the hood had a skull just like him, except instead of the skull of a human he had the skull of what looked like a deer; it's nose was elongated and it had antlers that somehow didn't stick through or pierce his hood.
Sans was speechless, in that moment he knew exactly who this figure was.
"Forgive me Sans, I didn't mean to scare you to death."
That joke made Sans chuckle a bit, but the shock of who was in front of him still had him dazed and confused.
"so… you're death then?"
Death nodded his head. "Were you expecting someone different?"
"nah, but I wasn't expecting you to be so bare bones."
Death chuckled again. "Making puns in the face of Death; if only others shared your courage my job would be much easier. Although I must say this place is full of brave souls, you should be rather proud of that."
While Sans was glad to hear that his friends didn't die afraid, talking about them made him feel… wrong. Especially with someone who was apparently there.
"You were going for a stroll yes?" Death asked. He motioned his arms, still hidden under his black cloak. "Come, let us walk and talk."
Death walked slowly, waiting for Sans to adjust to his pace. Once the two were walking in sync their conversation began again.
"so what exactly are you doing here? you got an appointment with me or something?" Sans asked.
"I am not here to take you yet, though I have taken you before."
Sans seemed confused, he looked up into Death's eye sockets as if asking for an answer.
"Yes Sans, I am aware of the alternate timelines, so I am aware of the pain that you must be going through now. Losing those you care about over and over with no end in sight… that is a punishment I would not wish on anyone."
Sans could feel Death's words pulling at his soul, he was bringing out the emotions that he tried so hard to repress. Every time he saw someone die he felt it but when you see the same person die so many times you try to make yourself numb to the feeling so that maybe it won't hurt so much the next time. But each time hurts just as much and it never gets any easier.
Sans tried to shift the conversation off him before he loses his calm. "you didn't answer my question. don't you have a job collecting souls or whatever?"
They reached the outskirts of Snowdin, the trees became less and less numerous and a cold wind began to blow.
"I normally do not set foot on the mortal plane, and even if I do it's only for seconds at a time to bring a soul to their eternal rest. The only reason I am even able to stay here is because this place is… special."
"special?" Sans questioned.
"This place is bathed in the blood of hundreds of monsters, living and dying again and again in one timeline or another. I return to this place countless times to pick up the same souls over and over, even if they are just hollow projections of themselves. Their constant deaths are what keeps me attached to this plane."
As Death finished his story they came past Grillby's restaurant and he decided that this would be a good place to stop.
"Grillby's. Care to make a stop?"
"it'll be empty." Sans said obviously.
"More room for us then."
Death opened the door and just like Sans said the restaurant was empty save for Grillby standing behind the bar and cleaning a glass. He almost seemed surprised to see them, though he didn't say a word.
"hey grilbz, how's it going?" Sans asked. "can I get a bottle of ketchup for me and…" Sans looked up.
"A drink. Alcoholic preferably." Death added.
Grillby nodded and went to work behind the bar while Sans and Death took a seat at one of the many stools that lay available. They sat together in silence until Sans asked a question.
"I didn't know death drinks."
"Even Death has things he'd like to forget. Besides, I don't normally get a chance to consume food or liquids; this is a rare opportunity for me."
Soon enough Grillby came back with their respective bottles, a large bottle of ketchup for Sans and what looked like a beer bottle for Death with the label "Hair of the Dog" on the front. He opened the bottle and took a swig from his awkwardly shaped mouth, the drink was tart and bitter but also had hints of sweetness and… hair.
Death looked inside the bottle. "There is literal dog hair in here. Who would have guessed?"
Sans nodded. "yeah, the dog patrol wanted to make their own special brew for when they were on watch. Then one of the dogs who makes the stuff fell into the mixing container and got his hair in a big batch of it, but somehow it became a big hit and now they use it as a staple ingredient in their brew."
Death laughed audibly this time, not a dark chuckle but literal bemusement. "Monsters are such interesting creatures."
"yeah… they are."
Sans finished off his ketchup and wiped some of the excess from his mouth, then he slammed the bottle on the bar and got out of his stool.
"thanks grillbz, add this to me tab will yah?"
Grillby nodded.
"heh, thanks." He looked back up at Death. "so… you ready to head out?"
Death got up as well. "Yes, I think I'm done here. Let's finish our walk."
Death and Sans walked out of Grillby's together and continued their stroll through the town. After walking past Grillby's they came to Sans' home where he now lived alone. Sans just looked at the house with sadness in his eye… sockets, he couldn't stop all the memories he had of his time here from coming forth.
"It's going to be lonely here without your brother, isn't it?" Death said more as a statement than a question.
Hearing that made Sans' throat constrict, sadness was beginning to well up but he didn't want to let it go.
"It will be rough for a time, that I know for certain, but you are strong Sans and I'm sure you will get by."
Sans had thought the same thing dozens of times before, now he stopped wondering if things were going to get better and just tried to survive day by day.
"You can't blame yourself for what happened to him, the child was going to kill him if that was their intention."
Hearing that though made Sans angry, how could he just say that this wasn't his fault? It was all his fault! If he had watched Papyrus more closely he wouldn't have died, he could have killed the kid before they ever got to Undyne or Alphys or… Toriel. But he can't stop them, every time he tries he's always too late, he's one step behind the child until they finally meet for their showdown. Sometimes he wins, sometimes he loses, but either way it's an exercise in futility and he just ends up back at home either way.
He was so angry in that moment that his eye flared with power, he wanted to kill this stranger, he turned around to try casting some of his bones but before he even had a chance his hand was grabbed by another bony hand and all the power seemed to drain from him.
Death's face didn't allow him to show any emotion but Sans could feel him staring deep into his soul and he figured that perhaps he had just made a serious mistake.
"Do you know what your brother said when I met him? He said that he was sad…"
Sans eyes went wide, how could he…
"Not because he was sad that he died, but because he thought that if he wasn't here you would never get up and do your job. He also mentioned something about 'never getting to taste his great spaghetti ever again'."
Sans… couldn't believe it. Even though he died Papyrus never lost his sense of joviality or innocence, he was so selfless and thought of others more than himself… and now he was dead.
Sans couldn't take it anymore, tears began to form in his eye sockets and he started to cry. He slipped his hand out of Death's grasp and fell to the ground, unable to bear the weight of this burden anymore.
But then something funny happened, while he lied on the ground crying for all the lives he couldn't protect Dearth leaned down… and he hugged him. He held the smaller skeleton for what felt like an eternity until he regained control of his emotions and the tears stopped. After he was finished crying he went silent for a moment or two and then he made a small, almost unnoticeable chuckle.
Death looked down at him and asked. "What's so funny?"
"death's embrace… it's comforting."
Death laughed at the insightful pun. "It is isn't it? People expect it to be cold and lifeless, but it's never truly as bad as you think."
The two skeletal figures got up off the ground, Sans wiped the snow off his jacket and the snow seemed to just fall off of Death's cloak.
"Do you feel better Sans?"
Sans sighed. "yeah, i admit sometimes this all becomes a bit much to bear but… i get by."
"Believe me Sans, you will be rewarded for your effort very soon either in this life or the next, that is a promise." Death extended a bony finger and made a cross over his chest. "Cross my heart… and hope to die."
Sans laughed at Death's joke and smiles up at him. "thanks pal."
"Now then, I have other appointments to keep and you have someplace you need to be as well, don't you?"
Sans sighed. Yeah… guess it's that time again."
Death extended a hand. "Come with me, I know a shortcut."
Sans grabbed the taller figure's hand and before he could blink they were standing together at the end of the judgment hall.
"whoa… how'd you get us here so…"
But before Sans could finish his question Death was gone without even a trace.
This made Sans chuckle. "guess even death has secrets."
And so Sans took his place at the end of the hall, waiting for the child to cross his path. Maybe he hadn't been given the best lot in life, maybe he did have to go through a lot of pain and strife, but he still believed that he would get his happy ending…
"cross my heart… and hope to die." He told himself.