A/N: This is something I wanted to start on a whim because I thought the idea would be cool. And. AND... I'm a sucker for both fluff and angst. This is probably gonna have both, as well as hopefully generous hurt/comfort. But we'll see how things progress! XD

This is based off a post I saw on Tumblr, involving Frisk truly meeting Gaster, discovering that he's Sans and Pap's father, and trying to get Gaster out of the void. I dunno if any of my theories or stuff for getting him out will make isense,/i but hey, this is my story and I'm stickin' to it. ;D

"blah dialogue blah" = speech
blah thoughts blah = thinking
'blah dialogue blah' = sign language
'blah dialogue blah' = sign language combined with Gaster speaking in Wingdings

This will be cross-posted between here and AO3, where my username is also Scriptor Bellum!

Surely none of the others would have let the child go back without wanting to accompany them.

Sans and Papyrus would tag along, one laughing at his own terrible jokes, the other talking about puzzles to drown out his brother. Undyne would carry the child through the ruins the entire time, refusing to put them down, summoning her spear at any sign of a threat. Alphys would trail along behind them anxiously, texting them every two steps, making almost constant suggestions to head home. Mettaton wouldn't even let them get that far, instead pulling them to be a guest on whatever show he was doing, ensuring that they couldn't go down there. (Napstablook would undoubtedly be in on that plan, to boot, making escape completely impossible.) Asgore would hold their hand the entire time, never going anywhere that seemed uncomfortable, insisting they turn back before they reached Hotland.

And Toriel? Oh, forget about that. Toriel would absolutely forbid them from going back into the Underground, and for good reason.

It was all empty now, without any monsters to be seen… well, aside from Asriel. But he was probably trying to stay out of sight, anyway, so it would be like there was nobody there.

There was something Frisk had seen down there, though – something that never really got resolved. Nobody ever talked about it, and yet, Frisk had seen it with their own two eyes! Why didn't anyone talk about it? Why didn't anyone talk about what was inside? … About who was inside?

It was a door that had shown up in Waterfall, almost out of nowhere. Frisk's curious nature got the better of them. When they went inside, the room was empty except for one thing, a person. Frisk wasn't sure who he was… or even what kind of monster he was. Or even if he was a monster! There were cracks in his face, and his features would have looked frozen if not for one thing. When Frisk had approached him, the monster's eyes widened, mouth going agape, before he just vanished into thin air.

Who was he? What was he doing in there? Why didn't anybody else talk about him? Did anyone know he was in there? For that matter… well… did anybody else even know about that door?

Frisk had never really gotten an answer to any of that.

Today, though, everyone else was busy. Today was their chance to sneak off to the Underground, go into that door again, and try to talk to that man again.

Everyone trusted Frisk to be careful by themselves, to make good choices, to do the right thing. And they were doing that, in a way. Weren't they? It wasn't like they could just leave that man behind if he needed help. Nobody else seemed to know he was there.

The thought of finally finding out the secrets regarding that door and that man filled Frisk with determination.

They were going to get to the bottom of this mystery one way or another.

As it turned out, finding the grey door again proved to be a little more difficult than Frisk had intended.

A flashlight, their cell phone, and a backpack filled with snacks had gotten them as far as the entrance between Snowdin and Waterfall. This was where they remembered seeing the door, but when they stepped forward into the other area, it wasn't there. Of course, that wasn't really a big surprise. They'd only seen the door once. After that, it seemed to have disappeared no matter how much they looked for it. Look they did, too… back then, and right now. There weren't any secret buttons or hidden levers.

Pretty soon, the child resorted to closing their eyes and spinning in circles. Maybe if they got dizzy enough, they'd wander around and find the door? It was kind of a long shot, and not a very bright plan. But it was all they had; beggars couldn't be choosers.

Dizziness kicked in soon enough, leading Frisk to stumble and collapse on the ground. "Mm… ousshhhh," they mumbled, shaking their head. Any words they spoke came out fairly garbled due to the fact that they rarely talked. It wasn't so much lack of being able to hear themselves talk as it was they just weren't used to speaking. While they could hear just fine, their voice didn't always cooperate. Rather than risk their voice messing up at random whenever they spoke, most of the time they'd just rather rely on sign language. Right now they had no one to sign to, and therefore no one would be around if their voice decided not to work.

They blinked a few times before glancing behind them, and their eyes widened in triumph. The door! There it was! It hadn't been there a moment ago… did this thing just show up whenever it wanted to? Hmph. Well, that was the way the Underground worked sometimes. There was no solution except to go with the flow.

The door opened just as easily as it had the last time Frisk opened it. In fact, it was almost a little too easy to get it open, as if some unseen force was pushing against it to get free. A wind blew past the child, whipping their short hair, and they took a step inside.

As soon as they did, it felt like their soul was being dragged down. It was the same feeling they'd got when Papyrus turned their soul blue, making them struggle to dodge his attacks. Except… this time, it was so much worse. It was hard to move at all, and were it not for Frisk's determination, they might have just crumpled into a heap right there. This was exactly how they'd felt when they entered the room before; heavy and tired and like it took all their strength to move. When they tried to call out, their voice failed them.

With a groan, they pressed forward. It should only take another couple of steps to see the man they'd seen before.

They seemed to give it a little too much oomph with their next step, because they tumbled forward and landed on the ground with a dull THUD that suggested, while disorienting, the impact hadn't hurt all that much. A hand rubbed at their head as they tilted their head up. The man… the man! There he was!

He was looking at them with one wide eye, the other one seeming to be permanently shut. Even with his shocked look, his right eye didn't open at all. While his mouth was hanging open a bit, it read just as stupefied as Frisk felt.

Frisk quickly pulled themselves off the ground, dusting at their shirt before staring up at the man. He was awfully tall… his face was completely white with the exception of his pupil and closed eye being black. The rest of him was black, too, and it looked like he was made of something that wasn't… all together. It would resemble a cloak, if it didn't look like it was melted.

It reminded them of the Amalgamates he'd found in Alphys' real lab, and their heart was struck with a chord of sympathy. Was he in pain like they'd been…?

'Hello!' they greeted happily, their hands moving quickly to sign out the next thing. 'It's nice to see you again.'

All at once, the man looked taken aback – not in the same way as he did the last time they'd seen him. He didn't disappear this time! Instead, his form lurched forward, the gooey substance making up his cloak crawling toward Frisk. For whatever reason, it didn't really scare them. The man seemed surprised and curious, but not malicious. After a moment of staring at the child, he lifted up his hands, signing back as well as speaking some distorted language that Frisk couldn't understand. '… You can speak in hands?' As he moved his phalanges (oh, was he a skeleton…?), it became clear to Frisk that there were holes in the middle of his palms.

The child nodded tentatively. Was he asking if they could speak sign language? Calling it speaking in hands was a way that Frisk had never heard it put before, although that had a nice ring to it. 'Yep! This is how I usually talk.' They raised and waved their hand around for a few seconds, trying to let him know that they weren't done talking but had to think about what to say next. 'If you don't mind my asking, who are you? What's your name?'

'Ah.' The man repeated their gesture, adding in his fingertips tapping against his mouth. 'My name is WingDing Gaster. Most people simply called me Gaster. What is your name, young one?'

'I'm Frisk!' The sign they'd made for themselves was a good one, they thought; a palm flat against their chest, then the same arm held out in an offer of friendship. It certainly fit them, if nothing else. Of course, they spelled it out before giving the sign for it, as Gaster had done. 'Are you okay in here? The last time I saw you, I think I scared you… sorry if I did!'

Gaster's face shifted from surprise to a smile, although it was muted. It was almost like he was afraid to give the child a real smile. 'No, no. Don't worry. You did nothing of the sort! It's just…' His fingers tapped against his mouth again, his head lolling from side to side for a moment. He seemed rather unsure how to explain whatever he was trying to explain. 'Do you know where we are?'

'Um…!' Frisk tapped one finger against their cheek in thought. What was this place, anyway? All they really knew was that it was somewhere that clearly wasn't a part of the rest of the Underground. 'No, actually. Do you know, Mr. Gaster?'

'Indeed I do. Child, we are in the void.' A second pair of hands, looking identical to Gaster's hands except made of blue magic, shimmered into existence. His original hands gestured to the space around them as the second pair continued to sign for him. 'It is a place where I exist, yet I do not exist. The rules are not the same here as they are in reality.'

Frisk tilted their head to one side, blinking a few times. Wait… what? That didn't make any sense. Not to them, at least. How could Gaster exist but not exist at the same time? '… That makes my head hurt.'

A ghostly chuckle reverberated through the room. It was clearly from Gaster, as his shoulders shook with laughter, and it wrapped around Frisk like a warm blanket. Whatever else could be said about this man, the sound of his laugh was comforting! 'I should think so. You're too young to understand advanced physics… and even most adults have trouble with the concept. Either way, you are not affected because…' His signing paused again, the fingertips of his magic hands pushing against each other. 'Because you were not actually erased from your timeline. You are a guest. I, a prisoner.'

'That's… terrible.' They meant it, too. What had Gaster done that was so bad he was completely removed from his timeline? As far as saves, loads, resets, and determination were concerned, it was easy to understand that. But Frisk had never heard of someone being erased from a timeline. How did that work? Was that the reason nobody seemed to mention him? 'I'm sorry.'

The smile Gaster gave them was much like the previous one he gave, only much sadder. 'Don't be, Frisk. I brought this on myself.' With that, he knelt down, the mass of his makeshift cloak surrounding the floor around Frisk. 'Might I ask, however, how you got here?'

Frisk pointed back toward where the door was. It was actually still wide open, since they hadn't closed it behind them. (Bad manners, but it had been an accident.) 'I came through the door!'

'The… door?' Gaster's face shifted, his eye flickering from Frisk back toward the door, then to Frisk again. It was almost like he hadn't actually seen anything. 'Child… there is nothing there.'