A/N: Alright, so after looking around on the site, I noticed that while there are a TON of Undertale crossovers, ones involving Higurashi are nonexistent. That's kind of strange, considering they both share a common theme of building friendships and solving problems without having to resort to violence. Fate and willpower play a key role in both series, but unlike Higurashi, where fate is something that cannot be changed easily, Undertale is all about taking control of the story yourself and bending it to your will, for good or ill.

With this in mind, I started coming up with the idea for this story after I realized just how similar Frisk is to a certain character from Higurashi. Those of you familiar with both series will know exactly what I'm talking about. If you don't understand, then I highly recommend watching/reading all of Higurashi and playing through the entirety of Undertale, as there will be heavy spoilers for both of them in this fanfic. With that said, enjoy my first ever fanfiction story!

Higurashi no Naku Koro Ni is property of 07th Expansion

Undertale is property of Toby Fox

Prologue: Curiosity

As I look upwards towards the sky past the now broken barrier, I can't help but feel a little nervous. While I'm happy that my adventure is over and the monsters are free, I have no clue what's in store for me now. After experiencing all that the Underground had to offer, including the other timelines, I've grown attached to it. But I've made up my mind, I'm leaving for good. I'm not leaving because I want to, though.

If I stayed, the monsters would be trapped down here until the next person fell down, if one ever did. Needless to say, that was not a risk worth taking.

"heya, kiddo. are you all ready to go? you gotta pretty important job to do now, being our representative and all." Sans said while waving to me.

"Just a minute, Sans. I have something I need to do first." I waved back as I turned toward him.

"oh really? what's so important that you have to hold up on leaving? you already said goodbye to everyone, right?"

"Just something I've been curious to see, that's all. I would've done it sooner, but there was a barrier that needed breaking." I shrugged as I started walking away. A thought occurred to me right as I passed Sans.

"Hey Sans?"

"yeah, kid?"

"Do you… do you think you could fill in for me as representative, while I'm away?" I asked.

"uh, sure I guess. why?"

"The thing that I'm going to see might turn out to be really interesting, so I could be gone for a while. In the meantime, someone needs to act as a negotiator between monsters and humans. You can't just wave hello and expect good results, you know." Considering how much effort it took just to make it this far, it would be a shame for everything to fall apart because of a misunderstanding.

"i get ya. so, why did you pick me and not somebody else?" Sans asked.

"Because you can understand people better than anyone. You were a judge after all. That and I wanted to give your lazy bones something to do for a change." Sans grinned a little wider than usual at my remark.

"hey, i'm not lazy; i just really enjoy doing nothing." Sans said, earning a chuckle from me.

"You just keep telling yourself that, Sans. Maybe if you put some backbone into your work, you'd have a skele-ton of free time later." We both laughed and exchanged some more bad puns until it was time for me to go.

"See you later Sans, take care of everyone while I'm gone, okay?" I reached out as we shook hands.

"you got it kiddo. don't take too long though, Toriel might get worried after a while; you know how much she cares about you."

"I know, I'll be fine. What's the worst that could happen?" I said, nonchalantly.

"heh... guess you'll see. see ya later, kid." We waved goodbye as I left for my destination.

Sans's workshop.

Okay... for the record, rummaging through someone's stuff is really rude, and I'd never do something like that to a friend. But, Sans was kind enough to give me the key to his room back at his house, and after looking around for a bit, I found the key to his secret workshop. If Sans didn't trust me enough to let me in there, then he never would've given me the key to his room in the first place. It's almost like he wanted me to see it. There isn't really anything too special in there, just a few blueprints for some strange devices that I don't understand, a picture of Sans smiling while surrounded by people I don't recognize, and a poorly drawn picture of three other smiling people along with the words "don't forget" written in lower case. But there's something else in here that I've never looked at before in all my time spent in the Underground, a machine covered with a sheet at the far end of the room. I had left it alone on the assumption that because whatever it was was covered, Sans didn't want me to see it for some reason.

But after a while, I got curious. What could be under the sheet that Sans felt the need to leave covered even though he let me in here? Could it be something he's working on that he's trying to keep secret? Maybe it's a failed experiment and he doesn't want to look at it. Or maybe, it's nothing at all and he was too lazy to remove the sheet before I came in here.

Knowing Sans, it wouldn't surprise me.

"Well, here goes nothing." I said, preparing for whatever might be hidden underneath the sheet.

I pulled the sheet off of the machine, and what do you know?

"I have no idea what this is..." I groaned.

At first glance, it looked like a strange walk-in shower surrounded by tinted glass without any pipes or a drain. The glass was frosted, making it impossible to see inside. Noticing a door, I open it and take a look at what's behind it.

Inside the strange machine is a monitor, a set of buttons, and a circular space on the floor that says "stand here." On the ceiling is some type of device pointed directly at the center of the place where you'd stand. Not a lot makes sense so far, but all of these things seem to be small parts of the machine as a whole. So what does it do, exactly?

"Well, only one way to find out..." I say to myself, stepping back outside and plugging the machine into the outlet in the wall. The instant the machine was plugged in, the lights in the workshop dimmed for a moment, and then a strange humming sound filled the room. Walking back into the machine, I shut the door behind me as I went to see what happened.

The interior of the machine was dimly lit with a soft, neon blue glow from whatever it was that was on the ceiling. The air itself seemed to shimmer and bend around it, as though the light was being sucked into a vortex above my head. In front of me was the monitor, now displaying a list of various places and a picture of what they looked like, with the buttons being used to look through the available options and pick out one for viewing. That's when it hit me.

'He's made a machine that lets you travel to different places.' I concluded.

I couldn't believe it. Sans found a way to leave the Underground, and he didn't tell anyone! Why? Why keep this a secret from everyone? Looking closely at the different places it could take me, I understood why. While some looked like they could be pretty easy to live in, others were very dangerous and outright scary to look at. But that wasn't all. Some things that should have been consistent in all of these places, like the color of the sky, did not match. Once more, while Alphys told me that humans were the ones in charge on the surface, several locations didn't look like people lived in them at all. There was even a place where gigantic, skinless things walked around eating people, nearly making me sick to my stomach. I'm sure that Alphys would've said something about those in her history books, but she never did. That left me with only one conclusion.

This machine wasn't just a thing that could take me to the surface, it would take me to a whole new world.

'There's so many of them...' I thought, looking through the different worlds I could visit. There were far too many for a normal person to see within their lifetime.

I guess it's a good thing I can SAVE and LOAD then. I have all the time I'll ever need.

After spending a while looking through the different worlds I could visit, I settled on the one that caught my eye. The picture that appeared on the monitor in front of me showed a small village in the countryside, which was set inside of a valley surrounded on all sides by thick forest and tall mountains. It looked like the most beautiful and peaceful place to live in any of the worlds that I'd seen so far.

I made up my mind, I'm going sight seeing. I'll be a tourist visiting from another world, how crazy is that?

After making a SAVE point so I could come back later, I highlighted my destination and pressed a big red button that confirmed my selection. In an instant, a blinding light filled the center of the machine, and the air became heavy, making it hard to breathe. Or so I thought.

I began to panic, because I realized that it wasn't the machine making it hard to breathe, it was the person that suddenly appeared and wrapped their arms around me, as if clinging to me for dear life.

"Don't leave me here! I don't want to be alone again!"

As I turned my head around, I saw a kid no older than me with red eyes wearing a green sweater with a yellow stripe across the middle looking at me with the same expression of panic I had. They buried their face into my shoulder as weightlessness overcame me and I passed out.

A/N: One thing that I see a lot of in crossovers is the use of some portal/gateway thingy in order to bring the two worlds together. Am I the only one irked by this? I mean come on, it's literally the most cliché way possible to create a crossover. It works well for series involving magic and sci-fi, but for everything else? Maybe I'm underestimating the difficulty in creating a plausible alternative to bringing two completely different universes together, but it bothers me nonetheless. Ironic, considering I'm guilty of doing the very same thing I'm complaining about by using a teleporter lol.

As it turns out, the reason I chose to bring Frisk into the world of Higurashi this way is because the true purpose of the covered up machine in Sans's workshop is never revealed, so everyone is free to speculate on what it might be. As for me, I'm utterly convinced that the machine is a teleporter, and I'll tell you why.

*SPOILERS AHEAD*

When you talk to the shopkeeper in Snowdin, she mentions that Sans and Papyrus just "showed up one day and... asserted themselves." Not much to go on, but should you decide to do the Genocide Route and fight Sans, he says this. "look, I gave up trying to go back a long time ago. and getting to the surface doesn't really appeal anymore, either." Notice how Sans is differentiating the two locations; they're not the same thing. So that begs the question: Where was Sans trying to go back to, and how did he and Papyrus wind up in the Underground? The answer is never given at any point in the game, so no-one but Sans knows. As far as I'm concerned, Sans built a teleporter to try and go back to his home world, and he either couldn't find it and gave up or decided that life in the Underground wasn't so bad after all, that's my take on it. What do you think?

Also, don't worry about future chapters being this short. As this was only the prologue, it only needed to be as long as it had to in order to set up the story, as a prologue is supposed to do. The first proper chapter will begin Frisk's new life in the world of Higurashi, and he won't be alone...

See you soon!