Leaving the Void

Prologue

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 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.