Every monster west of waterfall knew of the unresolved romantic tension between a certain skeleton and the owner of his favourite bar. Gossip was scarce in such a sleepy village, and the subject of the two was always a popular topic to discuss.
Given that Grillby was made solely of fire and Sans of bleached-white bones, neither had the genitals nor the desire to have sex. This alone obviously was not basis for a relationship, but there was no shortage of evidence to suggest that the two were "meant to be."
Papyrus, as Sans' brother, wanted nothing more than to see him happy. This was why when Sans came home hours after the bar had closed, his smile looking a little less plastic and a little more real, he didn't complain. Papyrus knew that some days, Sans couldn't find the energy to function, but spending time slumped over the pristine bar, a bottle of ketchup and a flaming-hot friend never too far away, seemed to ease a bit of the sorrow that Papyrus couldn't fix.
As Papyrus' best friend, Undyne knew all about the situation. She ranted and raved about how much of a wimp Sans was being- he should just ask Grillby out already!! However, much to her chagrin, Papyrus was too pure and honest to allow any scheming or trickery to sway the flow of Sans' love life. She grumbled, displeased at this lack of decisive action, and merely watched from afar as the rest of the townspeople were wont to do.
Alphys, being Alphys, found this situation to be the best thing since the invention of ramen noodles. Undyne couldn't help but gush over how "it's just like those awesome animes you watch!!" Alphys was inclined to agree, her gnawed-down claws trembling excitedly around her 67-page dissertation listing and explaining in excessive detail all of the possible ways they could set the pair up, using her extensive collection of human literature and movies for reference. She knew that Papyrus had said no, but she kept the plans anyways- just in case.
Once Mettaton's new form had made its stunning debut, he had traveled around to every town, immersing himself in the local culture for the day, casually mingling and definitely not showing off his gleaming chrome thighs to anyone who stopped to gape. This is what lead him to the dimly lit yet cozy and inviting interior of Grillby's, a stammering Alphys wedged as far into the corner of the booth as she could manage. "M-mettaton, I st-still d-don't underst-stand why I n-needed to come t-too..."
He peered over at her across the tabletop, his chiseled chin cradled in his gloved hands. "Why, darling, we haven't spent nearly enough time together! Also. I've heard such good things about this quaint little place-" he paused to witness Undyne and Papyrus enter, flanked by the entire Dog Division of the royal guard. "Oh! Undyne, Papyrus, darlings! Come join us!" Undyne's razor-tooth grin widened at the sight of her girlfriend, and Papyrus was simply elated that his favorite sexy robot remembered his name.
Their table became a hub of joyful banter and conversation, oblivious to the entrance of the shorter skeleton brother. He waltzed casually on over to the group to say his hellos before gracefully declining a seat- "nah, looks pretty cramped already-" and making his way up to his usual spot at the bar. Undyne enthusiastically prodded Alphys, who gasped and tapped Mettaton's shoulder. Mettaton look confused for a fleeting moment before Papyrus said, in his approximation of a whisper, "SANS AND GRILLBY ARE SIMPLY MADE FOR EACH OTHER- MY DATING RULEBOOK CONFIRMS IT- BUT THEY ARE TOO SHY TO DECLARE THEIR AFFECTIONS!" Mettaton's eyes lit up at the prospect of a good love story, and the group tried their best to maintain a level of stealth as they watched the goings-on over at the bar.
Grillby's flame flared a little brighter as he saw that his favourite customer had returned. [Hello, Sans. How are you today?] His hands gestured in front of him as he signed- fire doesn't exactly have the most functional vocal cords, and he had been surprised to learn that Sans knew sign language from the day the skeletons came to Snowdin. When Grillby spoke, it was like the sound of a gently flickering fire, which was hard to hear over the cacophony of the bar.
Sans grinned tiredly across the bar. "oh, yknow, same as usual- feeling pretty bone tired." In a casual disregard for the laws of nature, Sans winked, eliciting a quiet chuckle from the bartender. They fell into their usual exchange, quietly enjoying each other's company and sharing fries when Grillby had a moment to spare. Sans brushed off a squeal that no doubt had come from Alphys- the sound wasn't uncommon coming from her, after all. He did take notice, however, when Mettaton made the executive decision to confront him.
"Oh, you fools! Can't you see it? Can't you feel it?" Mettaton had somehow crossed the room and laid dramatically across the countertop in the span of 10 seconds as Papyrus yelped in shock and Alphys buried her face in her hands. Undyne leaped to her feet, thrilled that she could finally take action.
"Yeah! You wimps need to face the truth! You're perfect for each other! Everyone knows it's true!" Her hair flowed dramatically behind her. Alphys, emboldened by her girlfriend's actions, piped up from behind her claws.
"Sh-she's right!" Before she could continue, however, Papyrus stepped in.
At this point, every occupant of the bar was focused on the unecessarily dramatic scene unfolding before their eyes. Dogamy and Dogaressa silently agreed that this had been coming for a long time. Doggo, though he couldn't quite see what was happening, was glad that this whole mutually pining thing was being resolved. Greater Dog was panting with excitement, while Lesser Dog continued to play poker with himself.
Bunny, though she had always harboured a deep affection for Grillby, thought that this was better than the soap operas she liked to watch. She stared intently at Sans, who seemed utterly bemused, and Grillby, whose confusion was palpable.
"BROTHER, THOUGH I HAD NOT WISHED TO INTERFERE WITH YOUR LOVE LIFE, I, THE GREAT PAPYRUS, HAVE DECIDED THAT THIS CANNOT GO ON ANY LONGER! ACCORDING TO MY DATING RULEBOOK, YOU ARE IN LOVE WITH THIS GRILLBY FELLOW, AND HE WITH YOU!! THE SMILING!! THE SHARING OF FOOD!! THE WEARING OF CLOTHES!! ALL SIGNS POINT TO-" Sans chuckled, holding up a boney hand to halt his brother's monologue.
"bro. i know."
At least half of the room gasped. "Y-YOU KNOW???" Papyrus looked as if his jaw might actually detatch and clatter to the floor.
"uh, yeah. grillbz and i have been together for a while now." Grillby nodded to reaffirm this fact, leaning over the bar to brush his fingers against Sans'. "didn't you know?"
There was approximately 4 seconds of utter silence before everyone lost their shit entirely.