Welcome to a story that wouldn't leave me alone until it was written.
I do not own undertale or any related AU's.
Chara stood in the Last Corridor, waiting for their genocidal reflection. As they waited they thought back on their initial impressions of the human, they had met the human just outside the ruins, the prank with the ketchup had been great, and for a short while, Chara had thought that maybe not all humans were bad.
They were wrong.
They watched as the human killed Asriel without even giving him a chance, that had made up their mind that humans were untrustworthy. They had held a small amount of hope that maybe the human wasn't completely evil, but that was proven wrong when the human went on to kill every monster in Snowdin.
They had watched as the human carved a path of death through the underground, killing everyone from the guards, to the civilians, even killing Charas parents, Asgore and Toriel.
Chara was pulled from their sadness and reflection as they heard the door open. They looked up to see their genocidal reflection entering the room.
"Hello there," they greeted, "I wish I could say that it is nice to see you again, but that would be a lie."
Chara looked out a nearby window as their reflection glared at them, with knife in hand. Chara turned back to them and spoke.
"You know, I had hoped that you might be able to show the human race in a positive light when you first came here, but after seeing all this clearly I was wrong. So in revenge for all the Monsters you killed," Chara closes their eyes before opening them as red energy starts to flow from their left eye, "I'm gonna give you a bad time." They manifest knives of energy in the air an start throwing dozens of blades at their genocidal reflection, who clenches their own knife tightly in hand as they move out of the way of the blades.
As Chara launched blades at their genocidal copy, they could see them slowing down until eventually one of their blades cut through their opponents shoulder, drawing the first clear reaction from them in the whole fight.
"Fuck!" they yelled, "Well, you just gave me another reason to kill you my shitty copy, not that I needed one anyway but now I have an excuse to make it painful."
With a disturbing look on their face, the reflection lunged for them with their right arm hanging as the yelled, "You took my arm so I'll take yours!"
This confused Chara, both at being called a copy and the fact that their reflection couldn't use their arm. Chara had a decent knowledge of human anatomy, out of necessity, and they knew that the blade they launched didn't cut deep enough to sever any important nerves.
Chara launched another bunch of knives at the human, which were dodged. However as they dodged the humans right hand, that wasn't supposed to work, grabbed a blade that passed too close then hid it behind its owners back.
Chara was starting to get worn down though, so they couldn't spend any time wondering about it before dodging the swing of the humans knife.
Eventually the human knocked them to the ground, as the human approached they decided to ask a question to try and buy enough time to regain some magic to form more blades.
"Human," they said, "What did you mean when you called me a copy?"
The human laughed before responding, "Why it's simple, this world is but an alteration, one that shall disappear once I reset this world once again."
Chara frowned at that before speaking, "That doesn't answer my question."
The human laughed madly as they stalked closer, "Oh, it does, just think about it for a moment."
Chara thought through what they said before realising what it means, and the horror of that realisation showed on their face. "N-n-no, you cant mean..." they trailed off.
At this point the human was just a few feet away, "Indeed," a disturbing smile showed on their face, "I am the original Chara, and I'm about to wipe out a fake."
The human was above them at that point as they began to lift up their knife. As the human does this their right arm begins to move, showing the blade still in its hand.
As Chara saw this they spoke up to their reflection, "I should let you know something, before you kill me."
"And what is that?" their reflection asked.
"That knife that I shot into your shoulder, there is no way that it cut deep enough to stop any nerve signals to your brain," here Chara smirked "So if you can't feel your right arm, then there is something else stopping you from feeling it."
As they said this their reflections hand clenched the energy knife that it had caught, and as realisation flooded their reflections face the hand whipped around and plunged the knife into its owners heart.
"Damn...you...Frisk!"
The human dropped to the ground dead, with blood trailing down from the corner of their mouth.
Chara stood up as the human breathed their last, the energy from their eye stopped flowing as they dusted off their coat thinking about what the human had said, they had called out another name, possibly the person who had taken control of the humans right arm.
As they were lost in thought they didn't notice the darkness encroaching on them, consuming the Last Corridor.
Chara was jolted from their thoughts when they noticed the shadows at their feet, and they looked around to only see darkness. however this darkness was quickly broken by a beam of crimson energy, and raised voices that they could not make out.
They ran towards the direction of the beam in hopes of figuring out where they were. When they got in viewing distance they saw two humans fighting, one was wearing a blue coat and red scarf, while using what looked like the kings Gaster Blasters. The other was wearing a green and yellow version of what the human had worn, while wielding a knife.
The only other visible things were two floating buttons, one that said CONTINUE and one that said RESET. They were obviously what the fight is about but why?
They were pulled from their musings at a cry of pain. They looked back at the humans and saw the coated one on the ground, bleeding, while the other started speaking as they walked towards the button. "You may have gotten the upper hand this time Frisk but I will never allow you your happy ending, I will forever have my genocide!"
As Chara heard that they figured out two things; that the green-shirted human was the other Chara, and that they needed to be stopped. So Chara launched knives at their murderous reflection, forcing them away from the buttons.
Chara smirked at their growling reflection as they readied more knives. Their reflection glared at them as it asked, "How did you get here?"
"I don't honestly know, or care, all I know is that I won't let you kill this other human!"
As Chara was having a standoff with their reflection, they noticed the other child stand up, manifest their soul and start pulling energy together around it. Chara figured they were doing something so they attacked their reflection to buy the child some time.
The two of them struck back and forth, each trying to wear the other down, they split apart as Chara noticed the childs blaster manifest, strangely with a human soul within the mouth.
"Why are you even trying?" their reflection asked, "You nearly lost before, so why do you think that this time will be any different?"
Chara smirked as they responded, "Because this time I only need to stall you, not necessarily win."
Their reflection spun around when Chara said that, just in time to see the crimson beam from the childs blaster directly behind them, and then the beam consumed them.
When the beam faded Charas reflection was nowhere to be found, and the child was walking towards the buttons hovering in the void.
As they walked to the buttons they spoke, "I am aware that you may have many questions but the main thing that you need to understand is that you will be replacing that version of yourself from now on," the child stopped in front of the buttons and turned to look at Chara, "I don't know what changes that will make, but I do know that this will finally allow me to have my happy ending..."
Here is where the child held their hand out to Chara and asked them a single question, "Are you willing to see what lies in the original world?"
Chara hesitated for a moment before walking up and taking the hand held out to them while asking a single question, "What is your name?"
The child smiled as they responded, "My name is Frisk."
Frisk then placed their intertwined hands on the RESET button, which caused the black void to completely consume them for a moment, before Charas eyes opened, staring at a cavern ceiling whilst lying on a patch of flowers.
Chara looked around to see the Frisk sitting there in the same purple/pink shirt that the person who killed their brother wore. Though that made sense as it seemed that they had been possessed.
"So Chara, before we go anywhere I am going to explain the differences between this Timeline and yours."
So for my readers who were expecting me to post a new Generation STRQ chapter, sorry this was making me pretty much incapable of focusing.
BUT... now that this is written I will get the next chapter of STRQ up as soon as I can. Now this story is going to be a secondary thing, it has no set updates, it will be worked on when I get time or the compulsion to write for it, my main focus will be whatever story I am currently spending the most time on.
If I think my main updates are taking too long I will try to write a chapter for this.
In this story, AU's are essentially glitched RESETS which alter the world somehow.
The AU's used in this story are Storyshift and the very little info Smile run AU.
Look up Dirty Friend Killer by QueensDaughter on deviantart to see what frisk looked like during the load area and they still do have the blasters.
Also, I couldn't find any info on a Storyshift!Chara fight so I winged it.