In which there are dumb nicknames.

Sans, despite Papyrus's greatest attempts to rouse him by shouting through the door, missed dinner in the form of bread and cheese and something burned beyond recognition. Papyrus was still working on his cooking. Sometime later in the evening, no longer able to sleep, Sans got up and left the house for Grillby's, which was still open, the blaze of light from its windows visible from far down the street. Inside, it smelled of grease, soot and cleanness, inexplicably mingled into something warm and reassuring. Grillby himself, the source of much of the light in the building, looked up as Sans walked in. He was polishing a glass behind the counter—Sans almost never saw him still, if he wasn't serving, he was polishing something, and though the air was always filled with grease and soot, it never accumulated. Grillby was a fire elemental in neat, never scorched clothes; an immaculate white shirt and black silk slacks, vest, sleeve garters and bowtie. Even the crackling of his flames seemed neat and calculated. The place was quiet, only a few late talkers still sat at tables. Sans trudged up to the bar and pulled himself onto a stool. Grillby leaned over him.
".you're here late." His voice was a faint whisper of flame, thus necessitating the close proximity and relative lack of noisy atmosphere. Grillby usually communicated with gestures and sometimes, rarely, by an intimidating ruffle of his flames. Snowdin was small and peaceful, and any disputes that did occur could generally be resolved by this.
"Yep."
".don't drink that ketchup.I've got some put aside special for you."
"Thanks, I'm good on ketchup."
". really. what then?."
"Huh, what's that thing that's fried and has ice cream and cinnamon and basically everything?"
".that thing."
"That thing, the really good sugary thing. I want that."
".excellent."
It was a fried and still crackling dessert roll stuffed with honey cinnamon cheesecake, drenched in whipped cream and chocolate and nestled against a large scoop of melting vanilla ice cream. It was one of Sans's favorite things in the world, but he tried to refrain from eating it except on special occasions. Grillby watched him tuck into the concoction with satisfaction and let him eat for a while in silence.
". so. . that one didn't go well either." Sans choked on his food. How he managed this without possessing throat or tongue would make an interesting subject of scientific inquiry, but such is not the purpose of this tale. ".ah.I won't mention it. looks like another snow's starting, eh?.I just got the path nice and swept."
"Grillby, have I ever told you what an excellent monster being you are?"
".I believe it was understood.I am excellent."
"Yes, you are." Grillby leaned his arm on the counter and crackled with contentment, almost like a cat purring. Sans ate in silent concentration. The monster food melted, in a glorious glow of crunchy creamy cinnamon honey cream sweetness, into pure energy that rippled across his body, warming his bones and his very soul. He could never be really unhappy while eating this. He basked in the moment, trying to eat slowly, storing up feelings of wellbeing and contentment for the future. He felt he would need them in the next few days, and he was going to run short, as he couldn't possibly spend all his time eating. But it was good to get a break. After finishing he sat back and basked in the comforting ambiance of Grillby's, in no hurry to leave. If he stayed long enough there was a good chance he wouldn't have to walk home. Sure enough—
"BROTHER!"
—He heard the door open, energetically enough to send it rebounding from the wall with a crash. There was no sound of it connecting with the monster who'd flung it open, however, probably because they had already leapt inside.
"IT IS PAST YOUR BEDTIME!" Sans quickly searched for his wallet in one of the capacious pockets of his jacket. Ketchup residue, wrapper residue, dog residue—there it was—too late, Papyrus had reached him. "REALLY BROTHER ONE WOULD THINK YOU LIVED HERE INSTEAD OF AT HOME! HELLO GRILLBY, SO SORRY MY GREAT LOUT OF A BROTHER INSISTS ON LIVING AT YOUR ESTABLISHMENT! GOODBYE!" He threw Sans over his shoulder, spun, and marched back towards the door. Grillby made a sound that could have been laughter.
"Guess we'll have to put that on my tab," said Sans, and Grillby, too far away to speak audibly, made several quick gestures, signing already done. Sans just had time to give him thumbs up before being whisked out the door. Outside, a cold draft swirled snowflakes across his skull. He pulled his hood up and nuzzled his face into Papyrus' collar. He'd gotten over the weirdness of his baby brother being enormously tall and strong, and lately, it was reassuring. Paps could take care of himself now. Sometimes he took care of both of them, though he usually didn't realize to what extent. Sans thought it should stay that way. Papyrus was cheerful and carefree, able to focus on little things, like improving(?) his fire magic, and this cute little developing obsession with the Royal Guard. Sans liked to see him like that.
Besides. A concerned Papyrus was, frankly, an awkward and a clumsy Papyrus. He meant well, and he tried—dear God, he tried so hard it was infuriating—but he had no idea. So. At home, there was nothing wrong with Sans, except for a chronic sense of fatigue which, though not really the extent of his symptoms, could be used to explain away the others. Sans didn't stop doing things and lie on the floor because he suddenly had no desire to live, it was because he was chronically exhausted and shockingly lazy. And both of those were also true.

Several days later Alphys met Dr. Gaster outside the lab. Gaster, in the act of putting on his coat, shied sideways, horrified that he'd nearly stepped on her tail. "Hello!"
"B-bad day? You seem eager to g-get out."
"No more than the usual, really. How are you?"
"A-alright!"
Gaster paused. "You want to talk with me."
"I do." She climbed up the side of his coat and settled with one forearm through a belt loop and her thick tail shoved down a pocket for stability. Gaster hooked his arm around her to keep her from swinging and resumed walking. When walking at his usual pace, which was a bit fast even for someone closer to his size, it took Alphys about ten rapid steps to equal one of his.
"I mailed that stack of letters today."
"Good."
"And because I'm a nosy little lizard I looked at the names on all of them, and they're the acceptance letters for the new interns, right?"
"They are."
"I didn't see a skeleton name anywhere in there, which made me very relieved. Until I noticed that there was one less of the group than the number I thought you'd agreed on." Gaster said nothing. "Is something weird going on here?"
"Not weird, just…" Gaster pulled a letter out of his unoccupied pocket, and Alphys looked at the name on it with an expression that made Gaster very happy that she had no talent for fire magic—otherwise, it might have burst into flames, and he'd struggled enough with writing professional-sounding letters the first time.
"I knew it." Gaster shoved the letter and his hand back into his pocket.
"It's because I'm undecided. I need to see him in person again. If I have second thoughts, I can tell Sans that I've just come to tell him in person that he is no longer being considered for the job, and if not, I'll deliver the letter."
"Well, at least you're putting some consideration into this."
"Quite a bit, in fact."
"Alright, I trust you." But Alphys didn't sound particularly happy about it. "When are you going to deliver it?"
"Hm. I've been planning to for a few days, actually, and I just haven't—"
"Do it today. I've already sent the others."
"Alright, boss."
"OhforGod'ssake. Stop that."
"Right away, boss."
"Gaster!"
"Boss?"
"Doctor. Please stop."
"Alright, Nerdqueen."
"That's better."
"Is this your street?"
"Yes. Thank you for the ride." Alphys slide down the tail of Gaster's coat on the sidewalk, waved and started away. "Don't be stupid."
"Of course not. Haha."
"Seeya tomorrow."
"Seeya."
He found a ferry that would take him to Snowdin and sat looking at the address on the letter, which he'd already memorized. He had a feeling that the next few hours would be momentous in some way, but in what way, he had no clue whatever. It was unsettling. Almost as unsettling as memories of sliding through time and space, now that he was again alive in the conventional sense of the word. He flinched and quickly turned his mind to other, earthier objects.

At some point, things no longer had meaning. He knew what it was that mattered to him, but it didn't resonate. He existed in a state of calm nothingness. Occasionally he slept or ate, but not because he felt that he needed it.
"SANS."
This was a phase. It'd go away. Maybe.
"SANS?"
Sometimes he felt nothing, and sometimes he felt so very, very sick. Sometimes he thought it'd be more convenient for both of them if he just disappeared, quietly, without a trace. But that was impossible, and he realized that. Paps shouldn't have to worry about him.
"SANS, YOU NEED TO GET MORE SLEEP. WHAT DO YOU DO AT NIGHT, ANYWAY? YOU DON'T EVEN LEAVE THE COUCH THESE DAYS, DON'T THINK I HAVEN'T NOTICED."
"S'fine bro."
What had he been thinking anyway. The sentry job was practically too much for him, and he fulfilled those duties by lying in a pile of snow all day, or at least, for as much time as Papyrus would allow him to. He'd (almost) convinced Paps that his snow lounging was his way of cunningly lying in wait for anything to walk past on the path.
This was it. He was done. Putting in an effort was hard enough even when there was hope, and he'd been struggling to imagine that there still was any for some time now. He was going to spend his days lying in the snow for the rest of his life, and if his health was any indication, it (mercifully) wouldn't be long. "I'm fine, Paps. Sometimes I'm just too lazy to walk up the stairs. Heh. That's somethin, isn't it?" And Paps would tuck him under an arm and move him to his bedroom himself, expressing his disgust at Sans' lack of motivation. Sans quietly agreed.
"SAAAAAAANS!"
Welp. There were the feelings again. It was some rotten mix of rage, terror and misery, and it propelled him off of the couch and towards the door, eye flaring a sharp blue. Next thing he knew he was crunching through the snow in a random direction.
Odd, he didn't remember opening the door.
He found a soft-looking drift of snow and let himself fall on his face in it. The world went quiet and everything was white. There. Maybe this was like what it was to die.
He wasn't sure how long he lay there, but he was disturbed by a small, fluffy dog which dug his head free and danced around him, panting nervously. Evidently it was concerned that he wouldn't be able to breathe. Sans rolled onto his back and gave it a halfhearted pet, and it leapt away in high spirits. He sighed. His breath made no fog in the air.
Well this was accomplishing nothing. This was all rather ridiculous, wasn't it? Sans pushed himself up with a groan and shook the snow out of his hood. He was going to Grillby's.

A/N: This was going to be part of a longer chapter where more happened but I realized it was going to be very long indeed.

Story spoilers below? Kind of? Maybe?

So, yeah, Gaster's already been Scattered Across Time and Space in this story. There will be backstory about this! My logic about this is, we're told several things about Gaster: one, he "fell into his creation," two, "his experiments went wrong," and then there's the above. But. Nobody said these were all the same thing. Heck, all these could be separate mishaps. Maybe Gaster just has literally the worst luck. Any one of these could be the thing that finally killed/scattered/erased him, (or maybe he's still around,) and for once, I'm going to go with the scattered thing not being what actually killed him. Boss monsters can take a lot in the name of hope and compassion.