War soon broke out between monsters and humans.

The humans' jealousy overtook their morals, and they began to senselessly attack monsters, claiming they were a 'threat'.

Arial, being the strongest warrior, was sent out on the front lines.

Arial was on the battleground, fighting humans, when suddenly...

A sword pierced her armor.

She slowly fell to the ground.

A soft chuckle escaped her lips.

Her body soon faded to dust.

When the battle was over, and Arial didn't return, Gaster was sent into a spiraling depression.

He went onto the field where the humans and monsters had fought.

Gaster found Arial's chestplate.

He fell onto his knees, tears streaming from his eyes.

Gaster suddenly noticed something glimmering inside Arial's chestplate.

He touched the chestplate, moving it slightly.

Gaster saw... A small soul inside.

He picked it up, holding it in his hands.

Gaster curled up into a ball on the ground, sobbing.

A human sprinted up to him.

"Allow me to put you out of your misery, vile creature," they said.

Gaster lifted his hand, and lifted the human up high in the air.

He dropped them suddenly.

Gaster walked over to the human's body, seeing their soul now floating over their body.

Gaster had an idea.

Maybe...

If he put the human's soul with Arial's...

Gaster picked up the human's soul, and touched it to Arial's.

The soul quickly melted into Arial's soul.

Her soul looked slightly bigger, and slightly stronger..

Gaster's eyes lit up.

He knew what he had to do.

Gaster began slaughtering humans on a massive scale.

He had grown an extreme hatred for them, and wanted nothing more than to see them all exterminated.

Gaster killed more and more humans.

At first, he felt remorse, but soon... It was a subconscious urge that he had to fulfill.

Gaster eventually went back to the Underground, where all monsters had been banished.

He was only able to slip through the barrier because of all the human souls he had acquired.

Arial's soul looked healthy, and that was all Gaster cared about.

He hid Arial's soul from Asgore, not wanting him to take his precious Arial away.

Gaster began secret experiments on the side in an effort to make something that could resurrect monsters.

Gaster was finally about to test it, but before he did, he decided to leave a note incase it didn't work.

'To whom it may concern.

If my calculations are correct, this device will bring Arial back to life.

However, it will kill me in the process.

It is a sacrifice I am willing to make.

Arial, if this is you reading this, I love you.

-W. D. Gaster'

Gaster stepped into the machine, holding Arial's soul.

He was ready.

Gaster activated the machine.

Something... horrific happened...