This au was created by Undertale fanatic TheBiggestFanOfUndertaleEVER.
Ebony and Aster were brother and sister, and they fell into the Underground a little while before Frisk. Aster was as normal as any human could be, but Ebony was much different. She had a secret; she knew her ancestor had been best friends with a monster long before the monster-human war. She had found a secret passage in her old home that lead to her ancestor's library. She learned all about how powerful some monsters were, like her ancestor's friend, Slasher. Slasher was the Captain of the Royal Guard during the monster and human war. She tried to keep her friend, Dalia, or Ebony's ancestor, safe, but she died in the war. Devastated, she tried to keep Dalia's children safe by teaching them magic, but they turned on her and killed her. In one of the books, she had detailed descriptions of how to learn magic. For any other human, learning Slasher's level of magic would be near impossible. But Ebony had a special soul. It was grey, for willpower.
A grey soul is formed when a human or monster soul is leeched of it's normal property and replaced with a burning willpower, a substance close to determination, to do something. Slasher got a gray soul when she was filled with the burning desire to keep the peace between humans and monsters. The wizard got their gray soul when she was filled with the burning desire to keep monster kind locked away in the Underground.
Ebony got her gray soul, which replaced her old orange, or bravery, soul, when she was filled with the burning desire to contact the monsters and run away from humanity. These were the only three people known to have willpower souls. Ebony learned how to use telekinesis, like Sans. Both of her hands and eyes would glow grey when she used her magic. She could throw bright grey fireballs with burning black centers. She also learned how to summon a Reaper Blade, similar to Slasher's. A Reaper Blade was a 4-foot-long scythe. The blade radiated with grey magic, and it was made of gold. It could slice through a monster or human, destroying it's physical form and soul. Slasher was also a scientist, and in her book, she talked about how resets worked.
Ebony has a full understanding of resets, but she cannot reset herself. Similar to Chara, Ebony hated humanity. All the children in town would make fun of her and Aster, and her mom didn't even care she existed. One day, she read about how to get into the Underground in Slasher's diary. In less then 5 minutes, she packed a small backpack, took Aster by the hand, and climbed up Mt. Ebbot. Hugging Aster, she jumped straight into the bed of flowers. She was greeted by Flowey. He grinned at her and tried to say:
"Howdy, I'm Flowey! Flower the Flower! Welcome to the-"
He would never forget Aster's little giggle, and how Ebony looked him square in the eye and said:
"Is this the Underground? Are you evil?"
She summoned her Reaper Blade and glared at him. He just stared in shock, speechless, and disappeared. Soon after that, Toriel found the pair of them. She took them in and took care of them for a week. When Ebony tried to leave, Toriel tried to fight her. When Ebony summoned her Reaper Blade, Toriel relented and simply said:
"You are ready. But your brother is not."
After a lot of protesting, Ebony agreed, telling Toriel to send him to her immediately after he learned magic. She left the ruins, and was greeted by Sans, who was being visited by Asgore. Sans glared at her, saying:
"Speak of the devil. You ready, Asgore? We're about to be free."
"I guess I have to."
Asgore summoned his trident, Sans summoned his Gaster Blasters, and Ebony summoned her Reaper Blade. Asgore and Sans stepped shock in shock. Sans:
"What the hell? What kinda human is this freak?"
Asgore, with tears in his eyes:
"That...Slasher's blade. Went off to live with the humans. Called her a traitor...she was my best friend. I can't kill you human. If you will be part of my Royal Guard, I would be very pleased."
"Wait, WHAT?! You gotta be kidding, Asgore. T-the sun...and t-t-the stars...we were so close...I feel drunk. Welcome to the squad, I guess. Freak."
"Did anyone come with you? You would do well to tell the truth."
He pointed his trident at her and glared. Ebony nervously told him about her brother. He just sighed ok, and left. Sans gave Ebony one more confused look, and ran off. That is how Ebony became a part of the Royal Guard. She trained with Undyne, who became an older sister to her. Two years later, Aster showed up with fire magic, and Undyne made him a sentry. Soon all the monsters got used to the pair, and they even respected and befriended them.
"We are both humans, yeah? But I think I'ma little different. I'm more powerful. Just to warn you, I won't show you mercy cause we're the same species. I hate being human." Ebony, during her fight with Frisk.
Ebony was 12-years-old when Frisk met her, and she had a grey soul, for magic. She had a very fierce personality, but she was very friendly if you got to know her. She had long red hair, which she never put in a ponytail, and big green eyes. She usually wore a fuzzy brown jacket, a yellow t-shirt, a pair of grey leggings, and thick black rain boots. She lived with her brother in a small house, right by Sans and Papyrus's house. You would usually find her at Undyne's house, Grillby's, Alphys's Lab, her house, or anywhere in Snowdin and Waterfall.
She would occasionally get herself drunk on ketchup, her favorite drink, with Sans, and Papyrus would have to carry them both to his house and drop them on the couch. Her favorite person in the world is still her brother Aster, who she would die for. Since she got terrible or no food at home, she deeply enjoys Papyrus's spaghetti, which makes him really happy. Ebony also really likes to drink coffee and soda, and she loves to eat french fries at Grillby's. Some of her nickname's include Ebo, Ebb, Nyo, Blade, and Slasher.
If you have been going pacifist, you will fight Ebony a little bit before the Mad Dummy in Waterfall. She will be holding a cup of coffee and hanging around the dump by the Mad Dummy. During her pacifist fight, she will only throw fireballs at you. When approached, she will immediately engage in combat saying:
"A human? We can use this soul to brake the barrier! Undyne will be so proud of me! And Asty! This is for you, Aster!"
Her fight is 10 turns long if you spare her. If you spare her 10 times, her conversation will go like this:
"We are both humans, yeah? But I think I'ma little different. I'm more powerful."
"Just to warn you, I won't show you mercy cause we're the same species."
"I hate being human."
"What are you trying ta prove, kid?"
"I can't show ya mercy, sorry. Why don't you try to fight back, so l won't feel that guilty."
"You have been quite nice to all them monsters around here. They seem to like you."
"I don't know why. We are just traitorous humans after all. They showed me mercy, too. More than I deserved."
"You sure are very determined, human. Could you have the special trait of determination, just like the first human to fall down here? Bad things happened because of that brat. Nah, couldn't be."
"You ain't gonna fight, are ya?"
"Whatever. Undyne will deal with you."
She will then stop the battle and walk away.