Frisk haven't met undyne yet. Frisk had only visited sans and papyrus.

Your pov

You got your clothes after you took a bath. Right now, your going to a field trip to the space museum! You were excited since you really, really loved space! You dressed up and got your bag with your favorite, galaxy colored teddy bear! Your mom gave it to you on your 6th birthday which was only a few days ago. You put it in your bat as your parents walked to you."Okay (y/n)! Are you ready to go sweetie?" Your mom asked as you jumped up and down and nodded rapidly with stars on your eyes. Your parents chuckled and you heard the bus stop in front of your house. "Well, it looks like it's time for you to go honey!" Your father said as you ran outside and went in the bus. You sat next to a window and saw your mother and father waving at you. You waved back as the bus took off. You got your book about space and read it. You were really interested in space and you hoped that you can go there when you grow up. The bus stopped at some houses but you were too distracted by reading your book. You soon arrived as you got your bag and got outside of the bus. You closed your book as you put it in your bag and you went to your teacher. "Alright class! Welcome to the space museum! Don't mess with some stuff in it and stay close okay?" You excitedly said yes with your other classmates as you all went in. You gasped and looked around in excitement. Your teacher and classmates went to different directions as you went on your own, exploring the museum in wonder. You went into a door that led outside. You saw a spaceship!!! It was really big!! You went inside it excitedly and messed with some buttons and levers. You flicked a random lever as the spaceship vibrated. You got scared as your teacher saw and panicked. "(Y/N)! GET OUT OF THERE!" your teacher and some staff tried opening the door but it was completely shut. The others went in and tried to stop the spaceship but it flew. You cried as the others called for you. The spaceship was fast and it flew to space. You looked around and it was really pretty but you were too scared to even think of the scenery. You screamed for help and desperately tried to get out but, you can't. You whimpered as you heard some beeping and red lights flashed. You panicked and the top of the spaceship opened and the seat launched up with you. You passed out.

Toriel's pov

I went to the spot to see if there are humans that are going to get here. I was about to leave as I heard a crash. I looked behind me and saw a child with no oxygen tanks or even a space helmet. I quickly got her out of the seat and ran to my house. I got some oxygen tanks, a space helmet and a space suit. I connected the oxygen tanks on the space suit and the helmet. I got her bag off of her as I put the space suit and the bag in a child room. In my house, humans can breathe so I don't have to worry about putting it on now. I put her on the bed. She looks so young. I went to the kitchen and prepared a butterscotch cinnamon pie.

Your pov

You woke up on a bed. You looked around and saw your bag. You got it and put it on. You saw a spacesuit but, you can breathe so it's okay. You went out of the room and explored. You were still scared as you went to, what looks like a living room. You went to another room and saw a goat lady with a space dress. You screamed as you ran and cried. You hid under the bed you woke up on. You heard footsteps. "My child? Please come out! I didn't mean to scare you! I won't hurt you! I promise!" She looked under the end as you panicked and went to the wall under the bed. She looked worried. "My child. Please come out of there. I promise I won't hurt you." Her aura seemed, calm and caring. You felt like you can trust her. You carefully got out of the bed as she smiled and grabbed your hand. "Greetings child. My name is Toriel. What's yours?" "M-my name i-is (y-y/n)." You said as she giggled. "What a pretty name. So, let's go to the living room." She led you there as you both sat down on the couch. "Now tell me child,  how did you get here?" "W-well. I went on a field trip a-and I saw a spaceship. I-i didn't know t-that it can g-go b-b-but, I m-messed with it and i-it went up. I-i d-dont know h-h-how I can go b-back to m-mommy and d-daddy..." You cried as toriel Pat your head. "Don't worry (y/n). We can get you out of here. I will take care of you." Toriel said as you hugged her. "T-thank you... Mom..."

Timeskip to a few months...

You and toriel got along and you treated her as a second mom. She thought you some things and fed you some butterscotch cinnamon pie which you really loved. You both loved space and sometimes viewed it. You trusted her but you were still scared about the others monsters but the more you stayed, the more you got used to them. Soon enough, a human named frisk went in here. You treated her as a big sis. You both played which each other but, she had to leave. You were sad that she had to but, toriel comforted you about it and she visited sometimes. This day, you were excited because toriel let you venture off with frisk. She was worried but was also happy that you were happy. You got your space suit and bag as you hugged and waved goodbye to toriel. You and frisk went out of the door. You snuggled your favorite galaxy bear. It was a little bit chilly but besides that, it was okay. You and frisk walked and reached a bridge with some sort of barricade? You two kept walking but soon you got tired and fell asleep while frisk was carrying you.

You woke up on a couch without your spacesuit and there was a blanket on you. You saw your teddy bear beside you. You sat up and got your bear. You went to what looks like a kitchen and saw frisk and a tall skeleton. He looked a bit scary even though he isn't really facing you. You shivered as you went back to the couch. You sat there, kind of worried that the skeleton will hurt frisk. But, you saw frisk smile at the skeleton. You stood up and peeked in the kitchen again. You saw them laughing. Oh. So maybe the skeleton won't hurt frisk. "Heya buddy" you jumped and fell to the ground which attracted frisk and the skeleton's attention to you. You looked up and saw another skeleton. "SANS! DONR SCARE THE TINY HUMAN!" the skeleton yelled which made you more scared. You quickly stood up, got your bag and bear, and ran outside. You saw an igloo and hid in it, shivering. You hugged your bear as you peeked to see if they are there. You saw that they are not so you took this chance to run forward. You saw water. You still ran until you saw water and light blue flowers. There are also some fireflies. You still ran and ran and ran until you reached a fish house. You hid behind it. You heard some metal clanking and you looked up to see a fish lady looking at you menacingly. You trembled as she stomped near you. You got up and ran. She chased you as you ran and ran. You were exhausted from running so much. You made it back to the snowy place as the fish lady still chased you. You saw frisk and the two skeletons walking but you didn't pay them much mind as you screamed and ran as fast as you can. Your legs are giving up as you ran near a cave in a forest. You went in and hid behind a rock. You trembled and stayed quiet but sobbed. You heard metal stomping and saw the fish lady next to you. "Found you human." She said with venom and summoned a spear. You trembled as you put your hands in front of your face, bracing for the impact... Nothing came. You looked and saw the fish lady... Flying...? You looked behind her and saw frisk and the skeletons. The short skeleton's eye was flaming which scared you more as you ran more into the cave and hid behind another wall. "(Y/N)?!?" you heard frisk call as you whimpered behind the rock. You saw frisk near you and she found you. "(Y/n)!" She hugged you. You hugged back as you saw  the skeletons, especially the short one. His eye was still flaming. You whimpered and hid behind frisk. Frisk noticed that you were trembling and looked behind her. She saw sans and knew why. She tried to comfort you. "(Y/n), it's fine. He won't hurt you." Your trembling decreased but you are still scared. Frisk sighed and carried you and went to the skelebros house along with, of course, the skelebros. She put you on the couch but you didn't let go. "(Y/n), please let go. I have to do something. Don't worry. Sans and papyrus will watch you." You hesitantly let go and she went outside. The skeletons sat beside you. You trembled and went beside the taller skeleton. The short skeleton scared you too much. "OH HELLO TINY HUMAN! MY NAME IS THE GREAT PAPYRUS!" you jumped and fell off of the couch. "Oh! I'm sorry small human!" Papyrus carried you. "What is your name human?" "(Y-y/n)" "(y/n)? What a nice name! As I already said, I am the great papyrus! And that is my lazy but space loving brother, sans!" He showed you to sans. You tensed up and hugged papyrus. "Hm? What's wrong (y/n)? My brother isn't scary!" You hugged him tighter. "Hey, kid. Im not that scary. I promise." You still didn't look. "Human! Would you like to play with me in my room?" Papyrus asked and you quickly nodded. "NYEH HE HE!" he said as he ran with you in his room. You two played with action figures and shared some facts about space. You even read the book that you have in your bag and occasionally went downstairs to cook Spaghetti.

A few months later...

You and papyrus had got along well. You and frisk had met undyne and she seemed pretty scared about hurting  you and frisk but you three became besties! You also met alphys, napstablook and mettaton. Mettaton has quite the liking to you and always put in some clothes on you and you posed as he took some pictures. You and alphys are anime buddies along with frisk and undyne. You all love anime but sadly, you can't stay late with them. You,frisk and napstablook loved to make some music together! You really loved to listen to napstablook's beats. It was cool! You and frisk visited toriel occasionally and she will always surprise the both of you with pie and some new clothes. The clothes are knitted by her which you find incredible and you wanted to learn how but she said you need to be older. You and frisk always look into space and point out some constellations or just talk about space. All this time, you haven't really talked to sans. You just can't get your mind off of what he can do and how terrifying he can be. You also had a few nightmares about you and him fighting and him killing you which got you more and more scared of him. Today, papyrus is trying to get you to talk to him. "(Y/N)! YOU SHOULD REALLY TALK TO MY BROTHER! HE... IS REALLY SAD THAT YOU WONT TALK TO HIM..." papyrus said worriedly. Yes, you are now used to his loud voice. "B-but... He is scary and he might kill me!" You said. You didn't really have that much nightmares about him but, you still haven't out your guard down. "NO HE'S NOT! I WONT LET HIM! YOU AND HIM MIGHT BE GREAT SPACE BUDDIES!" "O-okay... I will try..." You shakily went to his room and knocked on the door. The door opened and you saw him. He saw you and his grin widened a bit. "Hey there kiddo. What do ya need?" "O-oh... I just want to talk." He let you in and closed the door. You both sat on the bed. "So, what do you want to talk about kid?" "I just want to say that I'm sorry for not talking to you and for thinking that you are scary." "No need to apologise to me for that kid. I understand. I do look pretty menacing if I activate my magic. I might even get scared of it when I see it if I'm your age." You hugged him. His jacket is pretty soft. "But now..." You let go quickly and stood up. "YOU WILL HAVE THE BEST TIME WITH ME!!!" you said and grabbed his hand with stars in your eyes. "LET'S GO!!!" The both of you went outside and let's just say that you spent the whole day with him. You both eventually got home. Sans was carrying you as you snuggled into his jacket. He put you on his bed as  he exited his room and slept on the couch. The next morning, you kept apologising for letting him sleep on the couch.

You and sans had been hitting it off pretty well. You treated him as your dad and he treated you as his daughter. You treated everyone as a family. You also met asgore recently and he met frisk earlier. You overslept and didn't noticed that frisk already left. You treated him as your second father but sans was the best! You two always spend time in space, looking at the stars as he thought you more about them. All of you haven't really found a way out of here and into earth but, it was okay. As much as you missed your parents, you always have another family right here. You will always love sans as your father and you will always do.