Once upon a time, two races lived upon the earth, in harmony; HUMANS and MONSTERS.
These two species lived in peace together. They respected each other and it was very common to see humans and monsters being friends. It was almost as if there was no difference between them.
But one day, a war broke out between the two races. This was a war created out of fear of the monsters' magic, and ended because of the humans' power.
The MONSTERS were defeated, and were locked underground by a magic spell. They were banished from the surface forevermore, leaving them with very limited space.
One day, many, many years later, a human called Chara fell into the underground. They were accepted by the MONSTERS and the royal family treated them literally like their own child.
But this child fell ill upon poisonous buttercups, and died a few days later.
Their final wish was to see the golden flowers from their home village. The village of the HUMANS who resided near . By this time the legend of the monsters was a myth, degraded as religious and simple nonsense.
Their sibling and best friend, Asriel, took them there by absorbing Chara's SOUL and passing through the barrier.
But the humans thought Asriel had killed Chara. The humans fatally wounded Asriel, leading him to die. He went back underground and died in his mothers arms. The kingdom was struck. Their king declared a war on the humans, and then their queen abandoned them in disgust.
Six more humans fell, but the MONSTERS showed no mercy to them after what had happened to Asriel, their royal prince.
The human children were shattered and their SOULS placed into a jar. Just One more human soul was needed in order to break the barrier…
But when another child fell into the Underground they seemed to have other ideas. Nobody survived their genocidal, ruthless onslaught, and the timeline was obliterated, leaving nothing
The world lay in darkness, nonexistent. But the darkness would not last forever. Soon, the anomaly's patience would wear out and a deal was struck.
It was time to R.E.S.E.T.
As the world stuttered to a start, Frisk found themself standing on the flowers; the ones from the start of their "journey." They were largely ignored and irrelevant in the first timeline and had no reason to think this would be any different. They wished the landing would have just allowed them to…
But they could not brood upon that. Frisk's body advanced into the next room, forgetting to expect a fake-cheery flower standing in their way. "Howdy, I'm-"
"Cut it, Flowey." Frisk briskly replied.
The flower looked at them, confused. Then his memories started to awaken.
"I'm sorry, Chara… I'll let you through… please don't fight me…"
As far as Frisk knew, Flowey thinking they were a psychopathic genocidal murderer was (ironically) completely harmless, and the arrangement suited them just fine. After all, they kind of were. So they walked into the Ruins, right on cue for Toriel's daily check.
Frisk decided to stop talking at that point. After all, why do anything when you don't really matter? Being able to talk but nothing else only magnified the pain, as a reminder of what they once were, of what they could once do. They had no intention to be the anomaly's slave, the anomaly's connection to the real world.
Their pain kept them unaligned.
So they watched as the anomaly advanced. The first SAVE point was reached; The shadow of the ruins looms above, filling you with determination. Frisk felt a surge of determination; it wasn't theirs.
Soon enough, Froggits and Whimsuns were all over the Ruins, creating a huge mess in the wake of Frisk's body. They all screamed for help; yet nobody came. Vegetoids, Moldsmals, Looxes, Migosps, all of them were killed without a second thought. As if they didn't matter, as if they weren't real.
And all Frisk could do was watch.
As Frisk lost their DETERMINATION, the anomaly collected it, and became strong enough to take out any non-boss monster with almost no chance of failure. So the anomaly succeeded. Until they became conscious they could never rebel, and until after they have rebelled they couldn't become conscious.
"Prove to me you are strong enough to survive!"
CHARA LV 4 HP 32/32
|FIGHT| |ACT| |ITEM| |MERCY|
…
…
21614
"Y… you… really hate me that much?" Toriel stammered. "Now I see who I was protecting by keeping you here. Not you… But them! Ha… ha…"
Toriel turned to dust.
Wishing to save your adoptive mother fills you with DETERMINATION.
Frisk was determined to not let this happen again... not after what Toriel did. They had to at least try to save her... that's the least they could do...
As a principle, DETERMINATION is a SOUL virtue, and those with DETERMINATION souls get power from it. Certain events can boost your DETERMINATION greatly, and therefore your power. At the start of UNDERTALE, Frisk's Determination is 1000, and yours is 2000. When Frisk suffers lack of control and a body, their determination rapidly drops, and yours grows.
And so Frisk's DETERMINATION rose steeply, until they felt completely committed to the task in hand.
Frisk knew there was only one way to defeat the anomaly; to have more DETERMINATION, or else increase your DT until it exceeds the anomaly's. They also knew that the only way to save Toriel was to R.E.S.E.T. And they knew that the only way to R.E.S.E.T was to have the most DETERMINATION.
Using their DETERMINATION Frisk escaped from their body, which was currently occupied by the anomaly. They knew their SOUL couldn't take control of their former body until it was unoccupied, because there would be no way to get their SOUL in the driving seat otherwise; Frisk knew there could be no fighting in their vessel.
Frisk needed a vessel to stop the anomaly, and knew where one was. Turning back, Frisk entered Toriel's body, which awakened immediately. They knew the anomaly was stronger, and that they still had the LV from the last timeline... but the real fighting wasn't going to happen on a battlefield, and Frisk knew that better than anyone.
The real fighting, the battle of determination, was going to happen inside their minds.