As fate would have this story begins after Frisk has saved everyone in the underground but to save Chara he had to commit the genocide route. In doing so, they corrupted Chara, but they spared Frisk the death deserved because they knew of their intentions. The path scarred them to the point where they blamed everything on Chara and told Sans this, and he believed them.  Sans told everyone about Chara, and they accepted them and shunned Chara, and sooner or slightly later they began to abuse Chara. Not physically thankfully but mentally and emotionally.

Chara had crippling depression due to the people who once cared for her are now abusing her mentally and emotionally. She stopped living at the Dreemurr's because of this. She lives by herself and to be honest, she is way too young to be doing that, but she does it anyway. She goes to a school where Monsters are the faculty. She tries to stay out of trouble, but it doesn't help that all the teachers pay her no mind when Bullies attack her and beat her down to the ground. She used to fight back, but that always ended up with her getting in trouble, and possibly Sans getting involved.

Sans was brutal to her, so she tried to stay away from them as much as possible. She almost couldn't handle everything. The one that kept her sane was Asriel. Despite everything, he was still her friend and she cared for him a lot, but she noticed that the bullies left her alone when she was near him. She smiled at that, but she was a bit curious about it.

So a day occurred when they were supposed to hang out, but Asriel wasn't there. So she waited for about half an hour, so she decided to look for him, and She found him hanging out with that asshole Frisk, and they were talking wrong about her?! She listened to them from the window.

Frisk: "So Asriel are you going to hang out with that thing?" Frisk asked Asriel.

Asriel: "Nah I make up an excuse as to why I can't, but can you tell me why I have to pretend actually to enjoy their company that murdering psychopath, I can't believe, I was their friend let alone their sibling?" He said with a disgusted tone. 

Chara lost almost all of her Determination in that instant and then ran away, but as they ran away she made some noise, and Asriel\ and Frisk checked on the sound. They saw Chara running away, and Frisk smacked Asriel's head.

Frisk: "Dang it Asriel, I had a plan to hurt her more, but you ruined it."

Asriel: "How was I supposed to know that she was there?"

Frisk: "Asriel do you know where they would go?" Frisk asked Asriel since they knew her better.

Asriel: "She would stay on the surface. The underground has too many bad memories in it." Asriel says confidently. Showing actually how little he now knew of his sister.

Frisk nodded before grabbing a knife and smirking as he walked outside and looked in the direction where Chara ran from.

(Timeskip 1 month)

It has been a month, and no sound or even a peep from Chara and she stopped going to school as well. Frisk has meticulously searched the surface within a mile radius. Frisk is frustrated that he couldn't find Chara but sighs and it's about to be an entire year since they freed the Underground and saved everyone. He decided  to take a trip down memory lane.

He grabs a stick and some bandages to make things more realistic, but he also brings a knife as well just in case he has to defend himself. He half climbs, and half falls into the underground and begins to explore the ruins and Snowdin, but as he walks through the waterfall, it seems like someone has been living here and not for very long. Frisk raises an eyebrow and continues forward, and equips their knife ready for anything. Suddenly Frisk hears the music of Memory playing in the distance. 

He doesn't run towards it instead he slowly stealthily gets closer to the music and sees Chara with a small smile holding an umbrella over the statue and letting the music play and smiling at the music. To her, this is probably her last ray of hope and her only source of happiness. Frisk grins evilly and backs away slowly and walks away thinking of all the evil plans he could make after learning this new information.

After he gained some distance, he runs back to the ruins and climbs out, and goes to grab a sledgehammer out of Asgore's shed. After doing so, he made his way again hoping that Chara would move out of his way but she was still there almost as if she is protecting the statue. 

Frisk pov

Well regardless it makes no difference, and now I'm going to crush her last ray of hope in this world finally, and with this, my revenge will be complete. I sigh, and I prepare myself to destroy the statue in one hit. I back up so I can have a running start. I get ready to run and it starts well but before I can swing it. Chara stops the hammer in mid-swing and shoves me away. She looked at me with utter regret and sadness. I scoff and prepare to turn again. She ends it midswing still but doesn't hurt me but instead she just stopping me from doing something that would her more than any wound would do. I smile as I pull out a knife and throw it at her and go for another swing to destroy the statue.

To my surprise, she deflects the knife and takes the swing. As the sledgehammer hits, I hear bones breaking, but she stands in front of the statue even after that attack. She is oddly silent and doesn't say anything to me.

I instead try to swing at her instead of the statue, but she nimbly dodges everything despite having a broken arm probably. As I swing the hammer again, I see the knife, and then I swing the hammer once more but also grab the knife and sheave it. I throw the hammer at the statue, but Chara stops it and tosses it to the side. I pulled out the knife and lunged at her she was in shock from the knife's reflection of herself. I pin her to the ground and attempt to stab her, but She stops me from doing that and turns the tables around, and pin me to the ground while putting the knife above my head looking directly at me.

"This is your last chance to leave me alone with the last ray of hope that you haven't taken away from me." She says with harshness in her voice as those are the first words she says to me in such a long time.

She gets off of me and lets me choose whether or not to go for it again. She has lost almost all of the hope in her eyes. She is hesitant about my presence as she should be. I throw my knife at her while grabbing the hammer and throwing them both at the statue. Then I shoot a blast of determination at the statue hoping to destroy it, and ... I succeed. However, suddenly Chara stops all movement and looks at the statue and the light that used to be there fades from her eyes. She walks over to the statue and falls to her knees and tears fall onto her knees in front of the ruins of the statue. I should be happy about this but I don't feel happiness, all I feel is regret and then I get an overwhelming feeling of dread.

"If I had known that this would happen. I would have taken your soul at the end of that genocide route. Instead, I believed that you were doing this to save me, but in reality, you are much worse than I could ever be. I was upfront and tried to stop you from saving me. I didn't want to be saved, but you didn't listen. I just wanted everyone to be happy. You tricked me into believing your lies and deceit. I should have ended everything then but now I was thrown into this world. I would rather have been on the surface where everyone treated me like dirt from the get-go and not be nice to me at first and then stomp me back into the dirt. So tell me Frisk was nice playing around with my feelings and slowly destroying my determination? Tell me did it make you happy to destroy everything I loved and cared about not once but twice?" She says as her eyes begin to glow red in the middle and the red of the eye begins to blacken.

"So go ahead have your brainless friends come and save you because you are worthless without them." She says to me.

I begin to panic as I should have and then I attempt to call people but when I try to call them but nobody came. I yell for help, but then I remember that I told everyone that I was going through the underground and not to bother me at all. Then I remember I forgot to call Papyrus and now I have no time for that, Dammit.

"Now let me introduce myself properly." She says eyes bright with renewed determination.

"Greetings, I'm Chara. The demon that comes when people call its name." She says with an evil smile.

"So Frisk are you sure you can handle me when I fight back, because now I will show you no mercy." She says as she gets walks towards me summoning a knife from seemingly out of nowhere.

Fear enveloped me as I backed away. I run away not expecting this to happen but Chara chases behind me. She is right on my tail but I am managing to outrun her just barely. I look back and run with renewed vigor.

"No matter what you do no matter where you go I will find you and I will kill you. It will not matter who you put me up against I will slaughter them all if I get to kill you, then it will be worth it." I hear her say as if she is whispering it into my ear.

I run faster as if a demon is chasing me which there is. I get to the beginning and I hear her footsteps closing in on me and I I try to climb out of the hole but all of the vines snap and I fall back down. I get up and I see Chara walking towards me slowly. 

https://youtu.be/MoSPPsWwz-4

"Do you hear it, Frisk? It's a lullaby for you. This will be the last thing you hear as I take everything away from you as you did to me but unlike you, it will be straight to the point and not torturing you endlessly as you try to survive with the little hope and determination you have left." She says as I hear her theme play towards me.

I equip the stick and ran straight towards her but then I run around her and try once again to call Sans. He picks up and he hears me panting as I continue to outrun her but I know this is only because she is allowing me to gain some distance.

Sans: " Hey, Kiddo what's wrong? You said you wanted to be left alone to remember the underground."

"Chara has gone berserk and is trying to kill me. Please help me I don't think I can defeat her." I say quickly as I stop and try to catch my breath after gaining some ground from her.

Sans: "Kid what did you do to her? She hasn't gone berserk or even aggressive after everything we did to her so you must have done something  pretty awful to provoke her." He said annoyingly logically.

Chara: "Come on Frisk why are you running away now? What aren't you trying to destroy everything single ray of hope I have like before? Or maybe you are going to slaughter all the monsters again to destroy my hope just like now? Or maybe you are trying to justify your actions for slaughtering all the monsters just to get your freaking happy ending? Tell me Frisk what are you doing right now?" Chara Yells towards me.

Chara: "Oh I see you are calling Sans to help you. Well, that won't matter in the end, If he attacks, then I'll kill him and then go after you. It will not matter who you put against me. I will slaughter them all." She says in a chaotic voice.

Sans: "Kid what the actual freak did you do to her? She seems like she lost all of her sanity. I'll try to convince the other to help you but I'm not sure if we can help you let alone want to." Sans says quietly.

I sigh as I continue to run away again. I look back as I realize that Chara is ready to kill me at any moment. As I run through the underground, I noticed that Chara was always right near me. I run past Alphys' lab and manage to lose her I think. When I passed it but just in case I kept running towards Judgement hall. Once I reached it, I call Sans to see if he was still coming. Right before I can call him, I see him and all the monsters here to protect me. I felt relief once I saw them.

Sans: "Hey kiddo you should run past us so, we can stop her here." He says with a weak wink as if he isn't sure that he could win this fight. 

I nod in relief and slight fear and I run past him, then I see Asriel out of the corner of my eye and I grab his hand and pull him after me. No, absolutely no I can't let Asriel die, even if there is a sliver of a chance of dying. The rest were trivial to save but Asriel took so much time and effort. I'm not letting all the effort go to waste. That was my precious time and multiple resets.

I tried to run but Azzy didn't budge and wanted to go back to help the rest of the monsters but then we heard a massive explosion and dust filled the air. I only hear gaster blasters, and spears along with fire and I hear metal clanking. My heart hits the ground all of them have already been slaughtered already in such a short time span?!

I guess all of the main monsters of the genocide route are fending off Chara. I sigh as I try again to get Asriel away from this fight but he is bent on fighting with everyone else possibly thinking that he could make the difference.

Then suddenly we both hear silence as I feel more dust in the air Underground. Fear seeps into my bones as I look at Azzy who is just as afraid as I am but he also seems determined to fight Chara. Thinking he has the right to make her pay or something? I don't know what is going through Asriel's mind.

"Where are you, Frisk? Don't you want to destroy my hope and dreams? Well sorry to say that everyone else is gone and now only you remain, well except for Asriel. Your trophy for all your hard work." I Hear a distorted voice say to me.

Asriel looks at me as if he betrayed him as I only thought of him like that. He ran towards Chara to stop her from attacking me. He runs into Judgement hall only to be blasted out of it and a knife deep in his shoulder. The knife is yanked out and Chara looks in my direction as she slits the throat of Asriel in a very clean motion making sure there is no pain with his death except for his shoulder.

"Common frisk let's finish what we started and end this cycle of pain and suffering. It will end with the person it began with." Chara says as she pins me to the wall. She lightly smacks the side of the blade against my face as I see her eyes bore into me.

Fear is all I feel now and now I look at her and what I did to her. It's unforgivable to the point that, now that I think about it. I don't deserve this happy ending. I don't deserve anything at all.

"You finally understand what I have felt the entire time. I am going to kill you and when I do I will let you reset and you will have one more chance to fix everything you fail than life itself for everyone in the Underground and Surface will come to an end in this timeline for good and I will travel to other ones so, be a good boy and do what is right because unlike me you have actual people who care about you." She says as she plunges the knife into my soul-killing me entirely. 

I feel the world surround me as I reset the world and with this as my last shot to finish this once and for all. I look up as I realize all the sins I have committed and all the pain I put her through. I will try my best to make it up to her or at least try to.