A/N: This is an Underfell AU fanfic, but there is some material that could be considered spoilers for the canon of Undertale, not to mention that much of this won't make sense unless you've played Undertale or watched a walkthrough.
Part of the Underfell fanon is that pretty much everyone in Underfell swears, but I didn't want to bump the rating up, so I instead used a Mad-Libs style of swearing. Everywhere an expletive is called for, I inserted a blank. You can fill it in with whatever word comes to mind.
"Ugh…" Mettaton groaned with pain as he tried to keep up the fight. His battery was at dangerously low levels, and he knew that the show was ending one way or another now. His overuse of his body had caused both of his legs and all four of his arms to detach: a testament to how rushed Alphys had been as she had tried to finish his body in time for this encounter. He looked down at his body, which all in tones of red, black, and a menacing dark steely tone, much unlike the silver chic body he had been promised when signing up for this project. Half of his face was unfinished, leaving black plating instead of light gray like the rest of his face, and his two eyes on that side were simply glowing points. Still, it was his body, and he was corporeal now; there was no going back. As his four eyes dimmed, he found it harder to see the child standing before him, yet, how could he surrender? Then again, how could he fight when he couldn't move and could hardly see?
"I'd better end the show with a _ bang," he thought, but it occurred to him that he had tried to do that very thing the entire show and that the unnaturally-good-at-dodging kid kept preventing the finale that Mettaton knew the audience wanted. "Then I'd _ better end the show with a final farewell," he decided. After all, he had failed, so, one way or another, this was the final goodbye. Either the human child would kill him (which he had to admit wasn't likely), or he would be deactivated for his failure, putting him into a comatose state. If only he hadn't chosen to become corporeal…
"Well, darling," he said to the human standing in front of him, "I'm afraid that we must take a quick break! After all, we've reached the viewer call-in milestone! I've never had this many viewers before! Now, one lucky viewer gets the chance to talk to me before I leave the _ Underground for good! Who will call in first…? Ah, here we go!" Mettaton accepted the call and said, "Hello, darling, you're live! What do you have to say to me and to the _ lovely viewers on this, my last show?"
"This is your last show?" the voice on the other end of the line asked, though it wasn't really a question.
Mettaton instantly recognized the voice, and a paralyzing cold feeling went through him as pressure not unlike tears built up behind all four of his eyes, despite the fact that he couldn't actually cry in this body. The voice was so quiet, yet full of steely confidence. Mettaton had always associated that voice with comfort and support, but now…
"Good," the voice continued with more steel than Mettaton had ever heard before. "I hate this show. Every time an episode comes on, I just want to smash my TV to bits, track you down, and punch you in your stupidly fancy new body. Hah! You became corporeal just for that shiny chunk of metal! You could have at least had some decency and picked a proper suit of armor like the rest of the family, but no. You had to let yourself become an experiment and a freak show."
"I-I… B-" Mettaton tried to speak, but the voice cut him off.
"This whole show is worthless. This is the last episode? I'm glad of it. You've had your fun, Metta. Now, come home."
Mettaton's voice felt dry, but he managed to say softly, "I will."
"You'd better. It's about time you did."
"Nap-!" Mettaton started to say, but he stopped as he realized that the caller had hung up. He closed his eyes to fight back the sensation of tears. It was about time. Actually, it was far past time for him to return home, and now… it was already too late. He was dead already, and he had no chance of returning to the life he'd had before.
Sighing, Mettaton opened his eyes. "I'll take another caller!" he exclaimed, trying to be cheerful.
"I _ hate your show. It's so _ melodramatic," the second caller proclaimed.
"Your show is literally the only thing worth watching on the entire _ Underground network, but that's not saying very _ much. Still, I'll be sad to see it go," another caller commented.
"Are you going to die? I want to see some _ death. Either kill the human or _ die already," a fourth caller demanded.
"Ugh, your shows are always the same," a fifth caller complained. "At first, they were interesting, but now they're just _ boring. I'm glad this is the last _ episode."
"No! Don't stop the show!" the sixth caller cried out. "I just love the tension and drama! I don't know what the _ I'll watch without you!"
Mettaton barely listened to them as the familiar voice kept echoing through his head. After ten callers had had their chance to speak, Mettaton cut off the caller queue. He took a deep, steady breath. "Well, I thank you all for your input, darlings. You've been a _ great audience!" he said rather quickly before cutting off the show, leaving just him and the human in front of him. "It's all for the best," he confided to the small being. "This form's power consumption is far too _ inefficient. In a few moments, I'll run out of battery, and I may never be recharged again, since I failed to kill you. Still… I can see greatness in you. Don't let any of the circumstances of this _ place ruin you, okay darling? _ knows that I could have been and done so much more in a better place. As it is… I just want to go back home, as I'm sure you do, so please, continue on. That little _ Alphys will likely no longer bother you, as she'll have me to berate and torture. Again, it's all for the best. You should get out of this _ place as quickly as possible, and leave… leave those of us who can't be saved, alright?"
"You can still be saved," the child said softly, and that quiet, gentle tone of voice brought back memories of happier times, when Mettaton still lived with his many cousins, and his closest cousin had had a more gentle tone of voice.
"That's a nice thought," Mettaton told the child as he sighed. "I doubt it, however. I failed my job, and I no longer serve a purpose. I… I never should have become _ corporeal."
"I'll save you," the child gently insisted.
"How?" Mettaton scoffed. "You'd have to reason with _ Alphys."
"I will."
"You're insane, darling. Just run. Get yourself out of this _ place while you still can, and hurry! Alphys will break into here at any moment."
"I'm not leaving you," the child insisted. The expression on the tiny human's face said it all: there was nothing that could possibly change the child's mind on this matter.
Mettaton was about to protest when the doors suddenly opened, and he saw the silhouette of Alphys as she strode into the room. He wanted to speak to her, but his low battery made it hard for him to make any noise beyond a gentle whine, and soon, he shut off completely.
Electricity flowed through Mettaton's robotic brain, awakening his spectral self through the bond of corporeality. Before opening his eyes, he prepared himself to face down an angry Alphys or Asgore. He briefly wondered why he was being reactivated at all before deciding that it must be because they had some punishment in mind for him.
"Open your eyes," a cold, quiet voice commanded, and Mettaton's eyes immediately flew open in surprise.
"Napstablook," he said breathlessly as he took in the sight of the cousin he had left so long ago. The black ghost floated just above the ground, as if to avoid getting dirt on their regally spectral form. Their eyes were tinged with a bit of red, which either looked comforting or terrifying depending on their mood. At the moment, their eyes looked mostly just cold, but there was a tinge of emotion that Mettaton could not quite place.
"Metta," Napstablook said, and Mettaton heard another tint of emotion under the cold exterior.
"I'm so _ sorry for everything," Mettaton said pleadingly, not quite able to hold back a sob as he looked over his long-estranged cousin, trying to make sure that they were really there.
Suddenly, Mettaton felt a slap across his metallic face and looked to see that Napstablook had delivered said slap. He briefly wondered how his ghostly cousin had been able to do that when he remembered something Alphys had told him: although ghosts could not harm physical matter and could barely interact with it, any ghost could make full contact with a body that was possessed by a ghost or that was fused with a ghost via the process of corporeality. In short, a corporeal ghost was vulnerable to physical damage from both ghosts and non-ghosts.
Mettaton didn't have much time to think about the science of ghost monsters before Napstablook gave him another hard slap across his face.
"Why?" Mettaton asked simply, though not accusingly. He knew he deserved far worse.
"You not only left me, you also broke your promise that you wouldn't leave me. Long ago, you promised that it would always be us, and that you wouldn't go and become corporeal." Napstablook gave a cold, unamused laugh that sent a chill down Mettaton's spine. The ghost-turned-robot wanted to get up and do something, but the switch that allowed him to move any part of his body below his neck was currently off, so he could only lay there, helpless, until Napstablook decided to allow him to be able to move.
Speaking of his body, Mettaton realized something: he only had two eyes. He directed these eyes down to look at his body and found that he only had two arms, as well, and the dark steel parts of him had been shined up to a silvery, metallic finish. His body was now far closer to what he'd always wanted it to be.
A third slap woke Mettaton out of his realizations about his body, and he looked back up at his cousin. "I'm… I'm so _ sorry for everything," Metta whispered. "I don't even _ deserve to live."
Napstablook looked surprised. "Metta, you… well, you're right, of course, but I'm not going to kill you. I finally got you back, and I'm never, ever letting you out of my sight again! Do you know how worried I was when I found out that you'd gone off to that… that psychopath that they call a Royal Scientist?!"
Mettaton only looked at his cousin in shock. He had never once in his entire life heard Napstablook raise their voice. That was one thing that set them aside from everyone else: they never swore, and they never raised their voice. In a world where everyone was used to swearing and yelling, a quiet, steely tone that only said what was necessary to say caught attention far more easily than colorful vocabulary and loud shouting. Still, hearing Napstablook raise their voice, even if it wasn't by very much, captivated Mettaton's whole attention in a way that nothing else had before.
He was even more shocked to see that they had tears in their eyes. "Blooky…" Mettaton said softly, unsure of how to react.
Napstablook turned away and let out a shaky breath. "Metta, I just… I'm just glad to have you home, alright?"
"I'm glad to be home, and don't worry. I'm never leaving you again."
The black ghost turned around with a suspicious look in their eyes. "You've promised that before."
"I've learned my lesson the hard way. Fame and fortune, especially in this _ awful, twisted world, aren't worth it."
Blooky gently reached behind Mettaton's head and flipped a switch there, which allowed Mettaton to move, and Mettaton hugged his cousin tightly. The weight of unsaid words hung between them, but for the time being, this was enough.
"I love you, Blooky," Metta said very hesitantly, as those words were taboo in that cold world that they lived in, and he hadn't said them since he was very, very young.
Blooky let the silence stretch for just a moment before sighing and saying, "I love you too, Metta."
A/N: I hope you enjoyed this. It's my first real attempt at writing Underfell. Please let me know how I did. I may post other Underfell stories in the future.
The credit for the Underfell AU goes to the community in general for those who collectively created the designs and fanon. This particular story was inspired by a comic that I found on YouTube, posted by Yuki Koi yuki. They credit the comic itself to hotlegmeme on Tumblr, though I couldn't actually find it on their blog. Basically, the comic ends with Mettaton committing suicide on TV, which I found to be rather unfulfilling for a pacifist Underfell route, since the main point of pacifist Underfell is to redeem the monsters, isn't it? Thus, I completely rewrote the story to fit in with a redemption arc.
As for the picture, I sketched it based off of one of the scenes in hotlegmeme's comic. I will admit to tracing for a base for it, but I did change it through three different iterations of the sketch, so I think it's fair to say that it's mine as much as any sketch of an Underfell design could be. Again, the original Underfell designs are community generated. (If you like the drawing, please, feel free to comment on it. I spent more time on the stupid drawing than the story, as I am NOT artistic.)