A/N: Okay, I've been dying to do this for a very long time. I had two other ideas, but this is the only that actually developed in a way that I am happy with. This is my first x Reader, so please don't freak out too much if it's not good. To be honest though, I'd love to hear your criticism about it!

___________This story is brought to you by Popato Chisps.

You hadn't seen Frisk for months. She had gone missing while on Mount Ebott, and when she hadn't returned, you assumed that Frisk had fallen down. You had given up hope long ago of ever seeing her again. So, you often spent your evenings in the same manner, no longer having the playful child to entertain you.

You had adopted the habit of sitting on your back porch, staring at the dusk sky. You would watch as the stars covered the blue velvety sky. As you looked on, you hoped foolishly that Frisk was still alive somewhere, looking at the same stars at you were.

That was a lie. You had done that all of three times. More often than not, you would only sit on your couch in your pajamas and binge on (favorite show) while shoving your mouth full of (favorite junk food). When you immersed yourself in the problems of people that didn't exist, it made your problems seem more trivial. You could almost forget you had any problems other than when to pause to take a pee break.

However, tonight was a rare night that you were actually sitting outside. The sun was beginning to set when, suddenly, a large tremor shook the ground. You also heard a loud explosion to accompany the shake.

Could it be? You turned to look at Mount Ebott's silhouette against the sky. A glaring light was being emitted from it. In fact, the light was encompassing the entire landscape. Then, it stopped. The barrier.

Monsters were going to come to the surface. You couldn't quite tell what you were feeling. Were you excited? Anxious? Or were you terrified?

__________________TIMESKIP BY DEM

For the past few minutes you had been watching the hordes of monsters crawl, walk, slither, and fly out of the barrier. Even though the battle between humans and monsters and the surrounding events were taught in history classes, you didn't really believe any of it.

But now, here were monsters, pouring out of a barrier that you never thought existed. A thought entered your head, "If there ARE monsters, is Frisk alive with them, too?"

You walked out of your house, wanting to get closer to see what was happening. As you strolled down the sidewalk, you saw something-or someone-come running from the barrier.

You heard a screechy voice coming from this person in the form of a shout of, "HUUUUUMMMAAAAANNNSSS!"

The figure continued to sprint before coming to a halt in front of you. Only when it stopped did you realize that it was a skeleton. He was wearing a white t-shirt with some sort of symbol, blue shorts , red boots, and a red scarf or cape tied around his neck.

"Hello human! I am the great Papyrus!!! I'm here to make a good first impression! Do you like spaghetti?" He said, rather loudly. He looked as excited as a little kid on their birthday. You however, only stood still in shock.

A skeleton was talking to you. A skeleton could talk. A skeleton could be alive. What the heck was happening?

However, before you could further question what was happening, another, shorter skeleton emerged from behind a building. He was wearing a blue hoodie and had his hands stuck in his pockets. A big, cheesy grin was plastered on his face. His mouth didn't move as he said, "Hey, Paps. You don't wanna scare the humans, do ya? Why don't you come back with the rest-"

Papyrus cut him off by saying, "But this human isn't scared! And they were about to say they like spaghetti!"

The shorter skeleton took notice of you and held out his hand.
"Heya, kid. I'm Sans. Sans the skeleton. I see you've met my brother, Papyrus."

You tentatively shook his hand. As you shook it, you heard a whoopee cushion. The skeleton chuckled and winked, "The old whoopee cushion in the hand trick. It worked on Frisk,too."

You smiled a bit, more at ease now with the friendly skeletons. Maybe if all monsters were like this, the integration wouldn't be as bad as you thought.

"I'm (Y/N)," you said. Slowly realization dawned on you. "Did you say that it worked on Frisk? You know a little kid named Frisk?"

"Yes! Frisk is the monster ambassador, and our good friend!" Papyrus said.

"Wait, does she have brown hair, (S/C) skin and wear a blue and purple striped sweater?" You asked.

"Yup," Sans replied, "They're  a good kid. Liberated the monsters. Sure helped us out a ton."

"Sans! Don't do it!" Papyrus shouted.

"A skele-ton," Sans finished.

"ARGHH!! Why do you keep making such terrible puns?!" Papyrus cried. You chuckled a bit before becoming a somewhat serious again.

"So, um, can you bring me to her?" You asked.

"Of course!"Papyrus said, "I, The Great Papyrus, Know exactly how to find Frisk! Do not worry, human!"

"(Y/N)" you corrected.

You followed the skeletons to the barrier, taking in the astonished stares of people that you passed. Some small children excitedly pulled at their parents' hands, trying to run to the two skeletons.

You spoke to them as you walked and learned about life in the Underground, and of how Frisk freed the monsters. You were amazed at how heroic and kind Frisk had been. Part of you still couldn't believe she was still alive. After all this time of believing your sister was dead, now you were ecstatic to know that you hadn't lost her.

Before long, two other monsters showed up. One looked to be a blue fish with the body of a woman. The other was a small yellow lizard-esque creature wearing a lab coat.

"Hey, Papyrus! What're you doing, making us chase you and then coming back, ya punk!" The fish lady elbowed Papyrus affectionately.

"Don't noogie the skeleton!" Papyrus complained. You and Sans both laughed at that.

The yellow lizard seemed to realize that you weren't quite the same as the others and said, "Um, U-Undyne? I-I think there's a h-h-human with th-them."

"Uh, hi," You said awkwardly, "I'm Frisk's older sibling. Papyrus said she's your ambassador and they're taking me to her."

"Oh, that's great! It's good to know the kid has someone to look out for them on the surface," Undyne replied.

"Look! Here comes the human now with Lady Asgore!" Papyrus exclaimed, tapping your shoulder exuberantly to get your attention.

Sure enough, you saw the familiar calm face of Frisk brighten up. She released the hand of the goat lady walking with her and ran forward shouting your name. You also broke into a sprint and captured the small child in your arms. As you picked her up you felt tears of joy and relief in your eyes.

You put Frisk down and smiled, "I thought that you were gone! I can't believe that- oh my goodness! I missed you so much! How did you even survive with the monsters?" you turned to the others and said,"No offense guys, you're all great, I'm sure."

"N-none taken," the lizard lady stuttered.

"Mom taught  me that the monsters weren't bad," Frisk said,"I made so many friends."

"Mom?" You asked. Your mother had died long before Frisk had even disappeared.

"I mean Toriel. I call her 'mom'," Frisk explained, gesturing at the goat lady, "And that's Sans, Papyrus, Undyne, and Alphys. Oh, you'll like Alphys, (Y/N). She's a bit  of a nerd, just like you! In fact, I'm pretty sure everyone is here. Except for Asgore. I don't know where he is."

"That's great, Frisk," you said with a smile. Then you got an idea,"Why don't you and all of your friends come over for dinner? I would love to get to know them all."

Frisk nodded happily, and you led the small group of monsters to your  house, hand in hand with Frisk, finally returned to you.
________________TIMESKIP BY LEGS

Despite Papyrus' insistence that he and Undyne cook spaghetti, you decided to order a pizza instead. The others had hinted to you that Undyne's methods of cooking spaghetti were quite...fire inducing. Since you didn't feel like being homeless any time soon, you kindly turned down the offer.

At the moment you were speaking to Toriel, whom had been the first kind monster Frisk had met.

"Really, Miss Toriel, I am completely indebted to you for caring for Frisk so completely. Without your guidance, I hate to think of what may have happened- or what she might've done," you said.

"Oh, please, (Y/N), call me Toriel. And it was no inconvenience to care for Frisk. She is such a dear child. To be frank, Frisk would've been fine on her own, Toriel replied,"Besides, she has all of these friends to care for her."

Sans had been standing nearby and upon overhearing the conversation said, "But how can you be frank if you're Toriel?"

Toriel laughed,"You know what I mean, Sans."

Papyrus had also been nearby and said to you, "I'm sorry about my brother, other human. He simply won't stop with his puns! I, however, am a connoisseur of fine humor. For example, other human... "

"(Y/N)," you corrected again.

Alphys shuffled over to you and tried to engage in conversation.  "F-Frisk told me th-that y-you like, um, a-anime. Have y-you ever heard of Mew Mew Kissy Cutie?"

"No, I haven't, actually. Is it good?"

Alphys gawked at you, "Is it good?! It's only the best anime ever! It's about a cat human named Mew Mew who-" she began talking so rapidly that you couldn't understand a single word she said. When she finally slowed she said, "Oops. I-I spoiled m-m-most of the show, d-didn't I? Sorry." The little lizard placed a hand over her face.

"No, don't worry. I'd love to see it!"

Undyne had also sidled up to Alphys during the conversation.
"Yeah!" She shouted,"We could all have a viewing party together!"

"Oh, and I could show you all (favorite show)!" You said excitedly. You couldn't wait to spend more time with Frisk's monster friends, especially since most of them seemed to be about your age (with the exception of Toriel) and they were all good fun to be around.

Speaking of Frisk, where was she? You saw her sitting somberly on the couch, looking like she was deep in thought. You excused yourself from the group and walked over to Frisk.

"What's up?" you asked.

"Hmm? Oh, nothing," Frisk said.

"You're sure? You look like you're intensely thinking. That's a lot of focus on nothing," you said, nudging her.

"No, really. I just feel like someone's missing... wait!"

"What, who is it?"

"Napstablook! And, hold on," Frisk looked past you, "Alphys?"

Alphys came over, "U-um, w-what is it?"

"Do you know where Mettaton is?" Frisk asked Alphys.

"I-I'm not q-quite s-sure? Oh. My. God. I l-l-left h-him at th-the l-lab! H-he w-was u-up-updating a-a-af-after a a f-few re-repairs! Oh n-no! Wh-what if he restarts when n-n-nobody i-is left u-und-underground!"

The rest had now come over to see what was happening. Sans didn't seem to care. Undyne was trying to calm Alphys and Papyrus was trying to calm Undyne. Toriel only had a polite expression of worry, and said "Oh dear."

Wait, who even was Mettaton? You asked as much. Papyrus's jaw literally hit the floor.
"Human! Mettaton is the most famous television star! And movie star! And chef! And dancer!" He shouted after reattaching it.

"Oh, sorry for asking," you giggled.

"Alphy here made him. He was built to be an entertainment robot. I personally can't stand the guy, but he is impressive. And he has a soul," Undyne said, putting an arm around Alphys's shoulders. Alphys blushed and smiled.

"Oh, and he is pretty hot in his EX form," Frisk added.

"Hot? How can a robot be hot?" you asked. You pictured a rectangle rolling around on a wheel when you heard the robot part.

"Well, his legs for one. And the hair," Frisk started to explain.

"That's enough, Frisk," you said,"Anyway, Alphys, if you're really worried, I could drive you to the barrier."

"R-really? Oh, t-thank you, (Y-YN)!"

"Can I come with you, (Y/N)? Please?" Frisk asked.

"Of course! After all, you personally know the guy," you replied.

"Can I join this mission? I have always dreamt of being in a human car!" Papyrus practically pleaded.

"If you want to, sure!" You said.

"But, if we bring Papyrus, there won't be enough room for Napstablook," Frisk said.

"Oh, um, Papyrus, what if I personally take you on a special drive around tomorrow? Would that be okay? I'm really sorry..."

"Hooray! I, The Great Papyrus, will be the best driver! I can already feel the sun on my skin, and the wind in my hair!"

He looked so happy that you didn't have the heart to point out that he had neither of these and that he wouldn't be driving.

So instead you stayed silent and nodded while Frisk dashed out to the car.

Alphys walked to the door with you. Before closing the door behind you two you said to the rest, "Don't finish the pizza without us!"

"No promises," Sans replied.

You drove to the barrier, taking in the crowds of monsters and journalists who were interviewing them. For the most part, there seemed to be little hostility or spite.  The monsters were happy to answer questions, and there were even some people taking selfies with the monsters. The entire place was buzzing with energy and excitement.

You parked the car and instructed Frisk to stay there. Frisk would have been more than happy to stay in the car and wave at friendly monsters that she has met, if she didn't need to use the bathroom so badly.

You took Frisk's hand and weaved through the crowds, trying to keep sight of Alphys's small form. Finally, you made it to what had once been the barrier that separated humans from monsters. Cautiously, you stepped through. Alphys guided you through hallways and corridors until you reached an elevator.

You stepped out of the elevator and walked across a bridge. At the end was a hotel. On the dark facade was a sign reading "MTT" in gold. The hotel was empty, so you strolled through. There was a fountain that you noticed in the center of the lobby.

"Why is there a statue of a calculator?" You asked.

Alphys blushed as if she was embarrassed.

"That's Mettaton," Frisk told you, "This is his hotel."

"O-of c-course that's j-just his original f-form," Alphys said,"It was only u-used 'til his, uh, improved body was completed. Or, well, s-semi c-completed."

You left through the front door, and Alphys led you through quite a few bothersome puzzles. After an eternity of sweating and hopping on steam pads you arrived at the lab. You admitted that it was fairly imposing.

You walked in and Alphys turned on a light. There was a giant monitor that showed Frisk on it. You also took notice of a cluttered desk and lots of anime.

"Frisk, you know w-where the bathroom is," Alphys said. Frisk nodded and walked in a different direction. Alphys turned to you and said, "I'll g-go get Mettaton. Y-you can wait h-here if you like." She hurried away.

You looked around the lab.
So this is the Underground, you thought to yourself. You couldn't believe that Frisk had managed on her own down here. Especially this heat. The air conditioned lab was a nice relief from the intense heat outside.

Frisk walked out of the bathroom. She dried her hands on her pants and asked, "So, what do you think?"

"Pretty cool," you said.

"Yeah, and this isn't even where the real science-y stuff happens." Frisk said.

You heard the sound of heels clicking on the floor. A deep robotic  voice said, "Alphys, dear, why didn't you tell me earlier?"

You heard Alphys reply, "W-well, nobody r-really expected this."

"It doesn't matter," the deep voice spoke again, "Now I can expand my fanbase to the surface! I will be everyone's idol! Can't you just imagine it, Alphy? Oh, we must not forget dear Blooky! He will live with us, won't he? You could make him a fabulous body as well!"

"Only i-if he wants m-me t-to," Alphys said, coming into view.

"Well, of course, Alphys!"

You now also saw the source of the voice. It was, in fact, a robot. But not the one you had imagined. He was very tall, and his synthetic black hair covered one eye. He had a bright pink chest plate, and bright pink stiletto boots. You couldn't say how, but he pulled it off. You assumed that this was the Mettaton that you had come to retrieve.

His magenta eye widened when he saw Frisk. He walked up to Frisk and quickly embraced her.

"Oh! Frisk, darling! What a surprise!" Mettaton said.

"Hi, Mettaton. I see that Alphys fixed you really good," Frisk smiled.

"Yes darling, all new! Completed with an extended battery life. Now I can remain in my EX form! It's just so, well, fabulous!" He twirled before he looked at you, standing behind Frisk. He walked to you.

"I don't believe we've met before, beautiful."
__________________________

Alright, so that's a thing now! Yay! I'm officially one with the Undertale fandom!