(Can't focus enough on my script, so have a little something I wrote at work. 

Starts off about 80 years before Reset.)

~

The Core's tubes were backing up again.

Gaster sighed as he looked over the notes from the last inspection. As if he didn't have enough to worry about with the souls. Of course, he'd known about the issue for a while now—you couldn't be the Royal Scientist and not know the status of your greatest work—but he'd hoped that one of the maintenance workers would have been able to take care of it.

He rubbed his temples with a sigh. If he didn't have the scars to remind him, he definitely would have hired an assistant by now.

But there was no time for that. He needed a quick fix for this problem. And that meant...going to the dump.

He hated going there. The thought of monsters having to subside on the humans' scraps to advance made his marrow boil. But, at times, it was the only option. They just had so much more at their disposal, so in times like this, it was a necessary evil.

So, setting aside his work on the soul containers and swallowing his pride, he made his way to Waterfall. Luckily, the odd hours he worked meant that there was rarely anyone else there, which meant he didn't have to endure the inevitable "Are you the Royal Scientist?" "Yes." "You built the Core?" "Yes." "I didn't think you ever came out!" "Well, I do on occasion." "I've never seen a skeleton before!" and so on.

So, shoes and socks off, trousers rolled, he set to searching, looking around at his leisure. An engine would be just what he needed...it'd save him loads of time constructing the vacuum he was planning to stop the blockage. Of course, that wasn't likely, but if he could find enough parts...

Oh, hello. What was this?

He stopped and looked over the large wooden box. It had a hole in the side, and a heavy lid locked shut.

How strange.

He picked it up with a small frown, finding it quite heavy. Something must be inside. Surely nothing too valuable...but, then again, humans didn't care much for value, did they? He carried it over to dry land, examining it. The hole, based on a possibly-unwise decision to stick his fingers in, had metal parts inside—oh, for a crank. But why would a box need a crank? Humans were strange.

The lock was tough, but between the rust and a hard strike with a rock, it popped right off. He opened the box.

Oh.

It was...some kind of machine, with a series of black disks underneath. Everything was a bit wet, but that was an easy fix. Now came the problem of what it did.

He set out to find the crank. Then, plans for fixing the Core completely forgotten, he gathered up his new find and went back to the lab.

~

It took the rest of the night and a good chunk of the morning, but he managed to disassemble and reassemble the machine, cleaning out the rust and mud. Once it was all put together, he sat and simply stared at it. For all of his work restoring it, he still didn't know what it did. Was it a weapon? The sharpest thing it had was a needle, but that faced down and didn't seem to be a projectile.

Well. There was just one way to find out what it did.

He took a deep breath, then stuck in the crank and wound it up. He paused for a moment, praying that he wouldn't end up blowing up the lab. He gritted his teeth and tensed as he pulled out the crank...

...and nothing happened.

He stared. The box was whirring, but nothing was happening. So what was this for?

Humans were strange and cruel, but they didn't make things that were useless.

He signed a few frustrated words at the box, then sat back with a huff. All that time spent for nothing. Just a stupid box that whirred. His gaze shifted over to the black discs. He picked one up to look it over; the words were faded from the water, but the actual disc was still intact, if a bit scratched. He looked closer at it. They were very thin scratches, as if they had been done by...

Oh, he was an idiot.

The disc was just the right size for the little circle in the middle of the machine. He set it down onto it, and he smiled a bit as it started to turn. Now, if he was right about those needle scratches, he just had to move the arm with the needle onto...

He nearly hit the roof as music came from the box. Trumpets and saxophones came bursting from the little box, like a whole orchestra was inside of it. He took the arm away from the disc, and it stopped. He put it back, and there was the music again.

Despite himself, he smiled. How exciting!

He took the needle on and off a few more times, then took off the disc and put on a new one. This disc was a little wobbly, so the flutes and violins on were equally wobbly. The sound was dependent on the discs then. But how?

Another disc. This one was a high, wavery voice—the disc was fine, the voice was not. He abruptly took that one off and replaced it with the first one.

Well, humans may be cruel, but even he had to admit this disc player was charming. Perhaps he could make some improvements and give it to Asgore. 

He took the needle off and shut the box. He'd play with this later. For now, he really ought to work on fixing the back-up at the Core.

~

For the first time in quite a while, Gaster was aware of how...quiet the lab was. It always had been, of course; mostly, it was just him, and he usually liked the quiet. But now it was...a little too quiet.

He paused in his work and tapped his fingers together. He couldn't stop and go out, not now. But...he needed some sort of noise.

His gaze drifted over to the player in the corner. 

No, it was a human thing. He had his limits, and using anything from humans was far past that.

But...well. It was a little fun. 

He stood up and made his way to the box, lightly brushing his fingertips against it.

No. There was plenty of Monster music. He would make his own record player and listen to that.

But this one was here. And he did like all the saxophones and clarinets in that one record.

And...it wasn't like anyone had to know.

So, with a small smile, he allowed himself to turn the crank again and put on the record before returning to his work. 

As his foot idly tapped in time with the music, he reminded himself that it was just this once he would let himself give in.

~

For the life of her, Alphys couldn't understand why Gaster used a record player for his music. There were so many more options now! Tapes and CDs and even phones were much better than the beat-up record he played over and over. Once, she even offered to re-fit the record player to be a normal stereo. 

Given the look Gaster had given her, she was still pretty sure this suggestion nearly got her fired.

It wasn't until the record--which was already on its last legs by the time she started--was scratched beyond repair that she understood. DT work forgotten, Gaster had spent nearly the entire day trying to buff out any scratches. But, as the day drew on, he finally had no choice but to give up. Over her welding, she watched him sigh and drop the record into the garbage.

"I-if you want, I could try to fix it," she offered as she pushed up her mask. He shook his head.

"No, no. It is all right," he said. "It was just a...er, guilty pleasure, I think is the term." As he sat back at his desk, he waved vaguely toward the record player. "If you would like to use it, go ahead. Perhaps you can find something interesting to do with it." 

Oh, of course! She was an idiot. As someone with multiple guilty pleasures, she should have recognized this off the bat. She puffed out her cheeks, a plan forming in her head.

"Um...well, I'll think about it," she said before pulling her mask back down.

~

He would never know how much wax was thrown out over the next few months, or that transferring music from digital files into grooves on a disc was ridiculously hard. He wouldn't know how much Alphys had anguished over what kind of music her boss would like.

But, just a few days before Christmas, Gaster was surprised as he saw a stack of new, clean records waiting by the record player, along with a little note:

we all have guilty pleasures. Enjoy! :) -A

So, making a mental note to thank Alphys profusely when she came into work, Gaster set the first record on the player and turned the crank. As drums and clarinets and saxophones and trumpets filled the lab,  he returned to his work, foot tapping as he let himself enjoy his guilty pleasure.