Hey guys! This will be my first multi-chapter Undertale fanfic! I told myself I wouldn't post another story until I had already written a fair amount of it out, but I decided to post the prologue to this story to see if people liked it. So, I hope you enjoy!
In this story, Frisk is gender neutral, but Chara is female. I think Frisk is female so I may slip up on the pronouns a few times.

~Emily Believes xoxo

Gaster had learned first hand that it was very easy to lose track of time when you were focused on something. Though, in this case, perhaps "focused" was too kind of a word; nowadays, with the current timelines, he was fretting every moment of the lives of those on in the Underground, constantly in a state of worry. He knew people would most certainly get killed, but the murderer always liked to switch things up, make people suffer in different ways, just so they wouldn't get bored. It was sickening.

He knew that timelines existed before entering the Void; that's what brought him there in the first place. He had always hypothesized many things about the power of determination, one of those being if humans had enough determination to manipulate time. He tried to build a machine and insert artificial determination inside it to test this hypothesis, but while creating it he managed to fall into that same machine and scatter himself across time and space, erasing himself from existence. He managed to trap himself in the Void.

The Void was less of a horrid vacuum of nothingness and more of an infinite dark room. It was seemingly endless in every direction, and from every direction came comet-like lights that followed the line of what would be the wall and floor. Those, Gaster had learned quickly, were timelines. The current timeline was always the largest, and the older they got, the smaller they were. Unless of course, the former Royal Scientist had saved them. Then they stayed roughly the width of his foot and trailed behind him wherever he walked.

Saving timelines meant he could access them at any time, not just if they were the one everyone was currently in. Though he saw every timeline, they tended to repeat often, so he saved the unique ones, the ones worth analyzing over and over for some sort of clue.

He had six full timelines currently saved. The first, and by far his favorite, the timeline where Frisk first fell into the Underground, changing things forever. They made his sons so happy. They changed things for the better. They freed everyone from the Underground. It filled him with hope that things might get better, but that was without mention of the other saved timelines. The next one was the timeline immediately after Frisk first reset after reaching the surface. Their intentions were good, he could tell; they wanted to meet their friends and make everyone happy again, but that's not what ended up playing out. He knew Frisk wouldn't dream of killing anyone. They wouldn't hurt a fly, but they had made a horrible deal with a manipulative, soulless child before Flowey even showed in the Ruins.

"Please, Frisk… I just… I just want to see my family again. I want to talk to them. Will you let me be in control, just for a little while?" Chara had said, faking emotions that her soulless vessel couldn't properly show, striking pity within Frisk. They of course agreed, wanting to make everyone happy. Little did they know that was the worst decision they would ever make.

Then, the genocide started. Chara had possessed Frisk at that moment, her power and determination growing so much with every single kill. And the more powerful Chara was, she could stay in control easily without having to worry about Frisk taking the reins. Ever since then, Chara was in control, finding new ways to kill and hurt everyone.

The next was unfortunately another genocide run as well, only, Queen Toriel and King Asgore were spared because, for a moment, Frisk's soul allowed Chara to retain the small bit of care she had for them… but once they saw what the child had done, they immediately rejected her and killed her. After that, Gaster concluded that no more genuine feelings ever surfaced.

The next timeline that followed was a genocide run as well, except, well… Sans, his son, somehow knew about the timelines. With the information he had, he stopped Chara in Snowdin and fought her there, only to lose once more and turn to dust… and that meant that he couldn't fight them later on in the Judgement Hall. Interestingly, however, in this timeline Chara spared Papyrus, and she seemed rather surprised to come face to face with him in the golden entranceway.

Gaster actually had two versions of this scenario saved. One where Papyrus had hardly changed, still optimistic, still hopeful that the human could be good…

"Human… I've seen what you've done… All the people you've killed… But still, I believe in you. You can change, I know you can! Drop your weapon, Human, please. I don't want to fight."

The other however… He had never seen the typically happy-go-lucky skeleton so… angered and somber. It was rather disturbing, actually, and he hated to watch it over and over, but such was necessary to dissect it.

"Human… That's what I used to call you before, when I thought you were human. When I thought you could change. But... you killed everyone! Undyne… Alphys… S-Sans. B-But But I refuse to let you kill King Asgore!

"I no longer believe in you."

The last timeline he had saved was one where Chara shockingly let Frisk take control. Frisk tried to make everything right, make up for their mistakes and tried to spend as much time with everyone as they possibly could. They especially made sure they spent time with Sans, who they knew Chara had emotionally hurt more than anyone. And finally, after Frisk thought they finally achieved their happy ending once more, Chara killed them. She didn't even need Frisk's soul to do so. With the soulless vessel of her old body, she killed everyone right in front of them.

Frisk was so relieved when they saw everyone alive and well, laughing happily in the living room of their new home. For that while, they all had to live under the same roof until Asgore could get a peace treaty settled with the humans. Finally, they thought, I have my happy ending back. Of course, that was before Chara showed up, and when she did, Toriel gave a gasp.

"Chara, my child… is that… really you?" she said, her hand covering her mouth in disbelief.

"Chara…?" Asgore repeated, looking at Chara, hoping that it was actually his adopted child.

"Hey, Frisk, this a friend of yours?" Sans asked.

"Oh, we're great friends!" Chara answered, not allowing Frisk to deny the statement. Her brown eyes suddenly turned red, causing confusion from all over the room. Confusion from everyone but Sans, whose eye (or the skeleton version of such) gained a cyan iris. But Chara knew his power all too well, grabbing a kitchen knife and throwing it at the skeleton, and that easily took away his one hit point.

It was only chaos from there.

"Sans?! B-Brother?!"

"C-Chara! You never… Oh, dear… what happened to you?"

"Does it MATTER? That little hell spawn just killed Sans!"

"I never thought it would come to this…"

"D-Don't fight! The probability of e-either of you winning is very s-slim!"

"Chara, please! I've already seen you kill them before! Just let me have a happy ending for once!"

Gaster had grown to hate watching the saved timelines; he hadn't watch them in a long time. He had all the information he needed from them.

He walked up to a light string of light, the current timeline, and tapped it gently with his finger. Suddenly, the light split open to reveal the current timeline… another typical genocide run. Watching the timelines was like watching a television show... a sick, twisted television show, for it looked like he was viewing them from a screen. But as Chara went on killing monsters as usual, Gaster noticed something… The sky above (though it was really the interior of the mountain they were trapped under, it was much simpler just to call it the sky) seemed to be… glitching.

"No... no, this is not good," Gaster said. He closed his view of the timeline, watching all the older timelines shoot off around him. He hadn't noticed it before, but they were starting to glitch as well. "It shouldn't be this soon." He stood, contemplating the situation. Too many resets. The universe had a limit to how many times it wanted to be reset, and they were so close to that limit that everything was starting to glitch. And when that limit was finally breached, timelines would start smashing into each other, mixing with… or worse, destroying each other. "I can't let this happen…"

He paused to think once more, sighing once he finally reached his inevitable decision. He tapped the light of the current timeline with his finger again, causing it to split open once more. Only this time, he stretched out the split light until it became less of a television and more of a list of the sequence of events. He went to the continuous growing end and shoved it into the beginning, causing the timeline to collapse into oblivion and the light to fade.

A forced reset.

Gaster never liked to interfere with the timelines, even if he didn't like the events that took place in them; doing such was far too risky, but this time, it was worth the risk. His world as he knew it was in danger; he was the only one who could save it, the only one who could make things right.

As a new bright light began to grow, Gaster tapped it and watched the new timeline slowly create itself. Once he saw that it was stable enough, he placed both of his hands on the split light. He felt the energy of the light consume him, engulf him. And before he knew it, he was hurled out of the Void and fell onto a small patch of golden flowers.