Hey Undertale fans! This is going to be my first trek into this fandom so please be kind. I have to say this game, like for a lot of people, touched my soul (pun intended) and like so many others, I have really felt deeply about the character Sans, and he has become one of my favorite video game characters of all time. And I guess that's why I find his relationship with Frisk is so interesting. Personally I'm okay with people having him and Frisk have a platonic relationship, but for me I just feel like there's more going on there. So I'm just going to give a heads up: I'm creating my Frisk as a female, if you don't really like that, I really apologize in advance, I find Frisk to be female in my interpretation. In my opinion, Frisk is left up to your imagination on whether they conform to the gender roles or just remain non-binary. This is also a Sans/Frisk pairing with Frisk being legal age (about 18 or 19). I wanted to state that because although this is my favorite pairing, I don't like the fact that Frisk could be considered a child, so I made her older. This story may take some dark turns depending on my feelings on the subject, but I will include a warning at the beginning if that makes anyone feel better. Anyways that's all I had to say on that! I just want one more adventure with my favorite monsters and I hope you will too! Knowing that I'm writing a new story fills me with DETERMINATION!

Darkness…utter darkness…besides the lone figure that stood before her. She was exhausted…the battle was draining and it seemed like finally…after so long…the ending she was looking for had finally came to fruition. Asriel had given up…and the souls were finally free so why did she feel this emptiness inside her? Like there was more she could do? Frisk reached her hand out to the figure as if, in vain, she could wash her sins away by the kind act of a warm embrace. Her soul vibrated against her chest and made her feel something she couldn't describe. Was it overwhelming relief or overwhelming guilt? She didn't know for certain, all she wanted was to make the world happy again. The world she fell into. The one where she had met everyone else. The one where she felt love…and LOVE. Her breath grew ragged as her hands shook and her blood washed from her face. Releasing the figure, she was horrified by the sight of not Asriel but Chara's devilish grin…along with several bodies lifeless on the ground, all of which were her friends she made in the Underground.

Rushing to them she grabbed their bodies and shook them, "Wake up! Don't give up! We still have to see the surface!" But as she shook their bodies, one by one they crumbled to dust leaving nothing behind. Toriel. Papyrus. Undyne. All of them, gone. Frisk felt her tears rush down her face, asking what she had done to deserve this. Looking at the last body, her tears starting to flood her vision but she could clearly see him. His blue hoodie and his pink slippers on his feet. She crawled over to him, sobbing loudly as she cradled his body to her chest.

"Sans…? Please, don't leave me!" Frisk bawled, wiping the tears on her face with her sweater sleeves. "I don't want to lose you too! I care about you…about everyone!"

Suddenly his body moved, his face turning to face hers. Frisk gasped seeing noting in his eyes but empty dark black voids. His brow bones furrowed in a hateful glare as he pounced onto her unsuspectingly and gripped his skeletal hands along Frisk's throat.

"If we're really friends, you won't come back…" Sans whispered in her ear. Frisk couldn't make a sound. The air was being completely closed off to her, "Did you ever think you could ever get away from what you did? You think that giving us a happy ending makes everything right again, kid? After what you did to me? To Tori? To my brother? No, it doesn't." Sans clamped his hands tighter around Frisk's throat as she tried desperately to wriggle herself away, "Isn't it a beautiful day, kid?" He said menacingly as his eye began glow blue and yellow. "To be burning in hell…" The bone he created punctured through her chest as well as his. And as she saw her HP dwindling down, she watched as her dearest friend gave up his life to save the world…

"NOOOOO!" Frisk screamed as she woke up from the nightmare she had experienced. She was drenched in sweat and her pajamas were soaked through. A quick evaluation of the room to see what she had experienced was another nightmare. Her hair was a mess, sticking to her face, and her breathing was erratic. It wasn't until she touched her face that she realized she'd been crying as well.

The nightmares were common but they weren't nearly as violent as this one. Two years after the barrier was gone, Frisk who was now 12, couldn't get wink of sleep despite trying her very hardest to. She was still haunted by things she had done to the others so long ago and she couldn't bear to see them in that state ever again. Especially Sans.

She knew the comedic skeleton was aware of the resets, and that when they were alone he would always say things that only she would understand. However, even though they were best friends, Frisk couldn't help but feel this overwhelming guilt that she was responsible for everything that had happened to Sans. That was painfully obvious from the get go.

Sighing, Frisk rubbed her face with her hands when she heard a soft knock on her door. Turning to the sound, Frisk saw Toriel's face, "My child? Frisk? I heard a scream." Toriel opened the door wider and was shocked to see her child's face tearstained and pale. She rushed over grabbing a handkerchief out of her pocket to wipe away her adoptive daughter's tears.

"I'm sorry…so sorry, mom…" Frisk muttered softly.

"Oh my child," Toriel rubbed the human's shoulders affectionately, "There's nothing to be sorry for. We're all here and we all love you. There's nothing to be afraid of. Though these nightmares are getting a bit repetitive."

Frisk shook her head, "I can't sleep, if I do…"

Toriel placed her hands underneath Frisk's chin to stare into her child's warm brown eyes. "You need rest, my child, we all do. If you'd like I could stay here until you fall asleep, or I could call up Sans. Would you like that?"

On a normal day, Frisk would welcome that, but today…today she felt a change in her heart and her soul. She could no longer remain there…here…she needed to protect her family…and if that meant to leave and never return…she would.

"I…I just want you to hold me." Frisk whispered.

Toriel smiled, "Of course, Frisk." Toriel laid on the bed with her child and cradled Frisk in her arms. When she was sure that Frisk had fallen asleep, Toriel climbed out of the bed looking back one last time and smiled at her sleeping form. Toriel gently closed the door behind her and after a few moments, Frisk opened her eyes and went to her closet to gather all of her things in a bag.

Sans was awakened by the sound of his phone vibrating in his jacket pocket the next day. Groaning, he slowly clutched the phone and looked at who was calling him so early in the morning. He was surprised to see that it was Toriel and accepted the call bringing the phone to speaker.

" sup tori. whats going on?" Sans asked.

"…Sans have you seen Frisk at all?" Toriel's tone sounded frantic, "I haven't seen her since last night, and I don't know where she is or where to find her."

"now tori calm down." Sans tried to keep Toriel from blowing a gasket, "im sure the kid's fine."

"No," Toriel's voice went from frantic to stern in a matter of seconds, "There's something wrong here. Last night, Frisk had a terrible nightmare, I heard her screaming a thrashing about…Her nightmares are bad but they haven't been this violent before. I think…I think she ran away."

Sans' tone grew serious, "did she mention anything about it? the dream i mean."

"No, she never tells me her dreams. She refuses to, says it's to protect me."

Sans sighed, "ill be there, tori, just give me a sec. i know a shortcut."

Within seconds, teleported to Toriel's home on the surface, a quaint little house on the outskirts of town, perfect for a growing child. Sans' thoughts were racing and he was trying hard not to seem worried himself. Sure he was worried that Frisk was in danger but he was more worried about the resets. His mind shuddered thinking about it. Perhaps Frisk had already broken her promise. Perhaps she found this world too boring…just like last time. He refused to believe that, it had been two whole years since the entire incident and she probably felt like this was the last one she needed to do. Sans at least hoped that was what she was thinking. He knocked on Toriel's door, which flew opened as quick as lightning.

"what happened exactly, tori?" Sans inquired.

"Well after she had her nightmare, I asked her if she wanted you or I to comfort her. You know how she is, she only feels comfortable around us."

Maybe cause i know about the resets and what shes been through, Sans contemplated, "anythin out of the ordinary, tori?"

"Nothing, she just wanted me that night. And when I felt her fall asleep, I just returned to my room. The next morning I tried calling to her and asking what she wanted for breakfast but I heard no answer. When I went into her room I found that some of her clothes were missing and her bag, as well as Frisk herself." Toriel sniffled, "I don't understand what I did wrong…"

Sans rubbed his friend's back reassuringly, "its not your fault, tori. im sure the kid is fine."

"Then why would she run away? Why doesn't she want to stay home? I thought I was being a good mother to her." Toriel sobbed. Sans embraced her trying to make her feel better, but he knew he wasn't the right person for this. Glancing behind Toriel he saw a peculiar envelope on top of a table near the entry way and pulled Toriel from his grasp.

"tori, did ya check your mail today?" Sans pointed it out. Toriel gasped and looked at the envelope inspecting its contents. She opened it up and in it was a lengthy letter that she read aloud.

Dear Mom,

I'm sorry, but I can no longer remain here. I know you wanted me to stay and be a good child and go to school with the other human and monster kids, but I can't do this anymore. You've always been the best mom that anyone could ever have, monster or no, but I don't want to hurt you. I don't want to give myself the chance. Please, give the rest of my things to the other kids in school, some of them need my junk. I won't need them anymore. And also, please tell my friends that I will miss them a lot, and I don't do this with much joy in my soul. I want to make sure that no one can ever be hurt by me again, and if that means I need to go, then I have to. I love you mom.

Love,

Frisk

PS: Remind Sans everyday that his jokes are funny, even when they aren't. His smile makes me so happy.

"…Oh Frisk. Why would you ever think that?" Toriel's eyes watered.

Sans couldn't believe it…she ran away because she was afraid to hurt them? But what would that accomplish. Picking up a distraught Toriel, he contacted everyone he knew to try and find Frisk and bring her home, but it seemed that there was no sign of the little girl anywhere. Wherever she had gone…Sans could never truly replace the void she had put in his soul….

Flowey laid on the flower bed grumbling to himself when a small figure approached him with a bag on her shoulder.

"Ahhhh, well if it isn't you." Flowey greeted Frisk with a smirk, "What? Is the surface too boring for you?"

"No, I just didn't want to…bother anyone anymore." Frisk muttered.

"Oh," Flowey grimaced, "So what? You going to annoy me? Well too bad, you already do you idiot!"

Frisk stared at Flowey with a blank expression, "Asriel…"

"DON'T CALL ME THAT!" He yelled, his vines wrapping around Frisk's ankles and a demonic face looking straight towards Frisk.

"Its who you are, Asriel, I won't call you Flowey." Frisk seemed unfazed by the whole ordeal as if she had seen this before.

"It's who I was, you idiot! Now I'm whatever this is!"

"Then I'll help you," Frisk blurted out

Flowey narrowed his eyes on the young girl, "Help me, what?"

"I'll help you…I'll give you back your life…."

And that's the prologue, hopefully you found that somewhat interesting! I enjoy comments and criticisms, so feel free to read and review!