My only one(undertale au x fem reader) oneshot

That one soul: flowerfell sans x reader

(y/n) POV

"sister, who's that?" I asked Frisk. She and I jumped Mt ebott. (o^o did I say it right?) We still survived letting flowey tag along and meeting this goat lady named Toriel. She let us out of the ruins even though she didn't want to. Now we were in the snow as Frisk grave to guy a handshake. She flinched back looking at her hand. "Hey, the old buzzer in the hand trick." The... Skeleton said. "Hey, I'm sans, sans the skeleton. You two are humans right?" Sans asked as we nodded. He told us that he didn't feel like capturing us, but his brother would if he caught us. "Okay we'll be cautious-" "SANS, SANS WERE ARE YOU?! I HOPE YOU'RE NOT SLEEPING AGAIN!" A voice yelled catching our attention. "Crap, uh, hide behind that conveniently shaped lamp." Sans said pointing to the lamp. Frisk picked me up and walked behind the lamp. Another skeleton came, but he was way louder. When he finally left I sighed. "Frisk he's loud and kinda scary." I commented. Frisk Pat my head. "Of course he is. He's suppose to be scary." Flowey said.

As we kept walking we saw some cold lasagna with glass in along with a microwave that obviously wouldn't work, but under that, was a bear trap. We got away from the strange contraction and moved ahead.

As we were walking I saw a something in the snow. I walked over to it, but it was also a trap and I was lifted by rope as a bell ranged. "FINALLY, I CAPTURED A HUMAN! NO NEED TO STRUGGLE. ONCE I GIVE YOU TO UNDYNE I WILL BE IN THE ROYAL GUARD." The tall skeleton exclaimed. "FRISK HELP ME!" I yelled  "THERE IS NO NEED FOR YELLING WEAK HUMAN. NO ONE CAN SAVE YOU." The tall skeleton chuckled. Soon the rope was cut and I was let go. Before he could get me, I felt my my sister pick me up. "I GUESS TWO HUMANS ARE BETTER THAN ONE." The skeleton said said before summoning bones and attacking us. Frisk pushed me out of the way as she got hit. "Sis!" I yelled running over to her. She coughed up blood as I tried to pick her up. "STOP RESISTING BIGGER HUMAN, IT'S NO USE." He said as he was about to attack one more time but I ran over to him and kicked his foot. For some reason it hurted him as he held his foot. I ran back over to my sister as she tried getting up. Suddenly she embraced me as the skeleton attacked her one last time. She calapsed on the ground as everything faded black and her soul was shattered. That was the last thing I saw.

I woke up back in the ruins as my sister was talking to flowey, but something was different about her. She had little flowers that littered her face. "What happened Frisk?" I asked tugging her shirt. "Well once I died, the world... Reset itself." She replied. "It's a mistake I won't make again." Frisk said picking me up.

Reset after reset, Frisk and I got to know sans better. He even protected us from his brother, but what really worried me was the buttercups that covered almost half of Frisk's face.

When we finally meet this king Asgore, Frisk pushed me aside as Asgore tried to fight her. When it was her turn, she chose was she always chose, mercy. Asgore didn't care and attacked her no matter how many times she pressed the mercy button. Every reset it didn't change either. It only made the buttercups worse.

"Sister please you don't need to do it this time. I will." I said with confidence. "Look kid how bout you set this out." Sans suggested. Frisk only shook her head. "I have to. It's the only way to free everyone in the underground." She said "Then how about I do it?" I asked in hopes she would agree. Boy was I wrong. "No your too young for it and you don't have enough determination to come back." Frisk explained as she weakly got up. She fell as sans caught her.

No one's POV

"I'll get you something to eat to boost your hp." (Y/n) said as she walked away to get some nice cream. "Sans can you promise me something?" Frisk asked as (y/n) was out of earshot. "Sure kiddo, anything." Sans replied. "Can you promise when I'm gone you would take care of (y/n) for me?" She asked. Sans sighed before giving her an answer. "Sure." He said. (Y/n) came back with a nice cream and gave it to Frisk.

Timeskip π^π

Frisk was defended for the last time, but there was no reset. (Y/n) was confused as she slowly approached her sister. "Frisk... Frisky.... Sister?" (Y/n) kept saying. Frisk weakly turned her head and smiled. Sans walked over too. "It's... Gonna be okay (y/n). You'll be back on the surface with everyone in no time." Frisk explained "Are you gonna be with me?" (Y/n) asked holding her sisters hand. "No, but I'll always be with you." Frisk said. Be now sans was crying as red tears covered his cheek bones. Frisk then died leaving her soul behind.

(Flowerfell is the most saddest and romantic au I know.)