Disclaimer: Dark Souls belongs to From Software. RWBY belongs to the late Monty Oum and Roosterteeth. I only own original ideas and/or characters.
Long ago in a land frought with many dangers including dragons, darkness, and demons, there once lived a god. His name was Gwyn and he ruled the land of Lordran. However a great plague was approaching and the darkness was consuming the light. This darkness was called the Abyss, and from the Abyss came Manus.
Manus was the first human, and was the cause of the Abyss. He let the darkness of the Dark Soul he had found in the First Flame twist him into a monster that oozed darkness from every pore. Although, he also created humanity in the process that mutated him. Gywn sent one of his most elite knights, Artorias to try and stop the spread of the Abyss. But the Abyss was just the start.
A plague started sweeping the land as the light started fading. Those inflicted were known as Undead and marked with a Darksign. Those inflicted were cursed to live forever, eventually losing all sense of sanity from dying repeatedly from various creatures and demons that now roamed Lordran. Gwyn had discovered that every human had a piece of the dark soul in them.
To save his kingdom from the undead curse, he decided to use his light soul to seperate the dark soul pieces from all humans. However, this process would take many years to prepare to cover the entire earth, so Gwyn went to the Kiln of the First Flame to prepare the technique. He left his city in the care of his son Gwyndolin, Executioner Smough, and the Dragonslayer Ornstein. After many years of waiting, many forgot the reason Gwyn left, only his son Gwyndolin remembering.
Many did not know in the first place and thought that he simply used his soul to extend the age of fire. Due to this the Primordial Serpent Frampt sought to find powerful undead to replace Gwyn since the fire was still fading. This tale begins when the Chosen Undead enters the Kiln of the First Flame and meets Gwyn.
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Korst had made it to the end of his journey, the Kiln of the First Flame. As he stared at the fog wall he thought about all the events that led him here. Oscar freeing him, coming to Lordran, meeting Solaire, ringing the bells, joining the Warriors of Sunlight covenant, meeting Frampt, and obtaining the Lord Souls. He also remembers meeting his love Priscilla the Crossbreed.
He was a knight banished from his homeland for a crime he didn't was a crossbreed imprisoned in her own world with faceless assassins guarding her world. He felt a connection with her through their similar experiences and asked her to come with him back to Firelink Shrine. However, she refused since she had lived in the painted world for most of her life. Korst was heartbroken since he knew he had a duty to fulfill and couldn't stay in the Painted World. He left by giving her the lost doll he had found and in return she gave him a kiss upon his crown before he left for to obtain the Lordvessel and Lord Souls.
He gripped his greatsword that he had found off a corpse in Anor Londo with his hand covered in the matching armor of the knight Black Iron Tarkus. He had met the phantom of the knight earlier while facing the Iron Golem in Sen's Fortress. He now wore it after finding what had happened to the knight.
After his reminiscing was over, he entered the fog wall. He was there, Gwyn standing next to the First Flame. This god is why Korst had went on his journey in the first place. He had lost so many friends on the way, he was ready to finally finish it with the last fight. That is when Gwyn spoke.
"Greetings young Undead," Gwyn spoke in a rasping tone "I see that you have reached the Kiln despite the odds stacked against you."
"Why are you speaking with me instead of fighting me?" Korst questioned in a deep voice.
"It is because I have no intention of fighting you." Gwyn answered simply.
"How are you still sane after linking your soul to the first flame?" asked Korst with a confused tone.
"Linking my soul? Why would I do such a foolish thing?" Gwyn replied.
"But the serpent said that you had linked your soul to the First Flame to extend your age of fire." Korst said.
"First boy, I have learned not to trust the serpents that linger in the dark. Second linking my soul the the Flame would only delay the dark." Gwyn explained.
"So why did you come here?" Korst asked.
"To prepare a more permanent solution to stop the age of dark." Gwyn said.
"How would you accomplish such a thing?" asked Korst.
"Since humans can become undead because of the shards of darkness in their soul, I shall use my Light Soul to cancel out all darkness in the world." Gwyn explained.
"Then what of the Abyss?" Korst asked skeptically.
"The Abyss is nothing but darkness, so I shall give humans extra powers of light to combat the darkness of the Abyss." Gwyn replied.
"What of hollows?" Korst questioned.
"They shall be returned to a young state before they recieved darksign due to the shards of the Light Soul I will implant in them after driving out the shards of the Dark Soul. This will also give them the protection and healing properties of the Light Soul."
"What of the demons in Lost Izalith?"Korst continued his questioning.
"I was hoping you could deal with that actually." Gwyn said.
"Why me?" Korst asked skeptically.
"I was originally going to ask Ornstein before my soul was spread amongst humans, but since you have defeated both him and Smough I think you are more than qualified." Gwyn explained.
"If I am a human I will not be able to wipe them out." Korst said.
"Then I shall infuse a larger portion of my soul into you so you may have enough power to accomplish this task. As for Nito and his kin, they will not be able to survive the absence of the undead. The necromancers that keep them all alive are undead, and Nito has expended too much power. Without his citizens he will wither away in his slumber."
"Then I shall accept the task given to me." Korst replied.
"There is one more thing you should know, the power that I give you will put you to sleep for many years after the task is done. I am not sure how many but I do know that everything and everyone you know will no longer be the same. Take this into account after you wake up from your slumber." Gwyn warned Korst.
"I thank thee for informing me, I will keep this in mind when I wake up. I will now leave for Lost Izalith to deal with the demons. I am slightly confused by this, but I have no complaints if you can cure the curse of the undead." Korst said in response.
After this encounter Gwyn activated the ritual and everything was in chaos for days due to everyone reverting to humans. They slowly figured out what was going on and started to rebuild society. Meanwhile, Korst ousted the demons in Lost Izalith using the high powered protection and healing granted to him by the power of Gwyn's Light Soul shard. After finishing every last demon he could find he trekked to the Crystal Caves to prepare for his slumber.
It would be many years before he would wake back up and interact with the society that grew while he slept. A great evil arouse during his slumber. Gwyn did not think that the darkness he drove out would coalesce into creatures of pure darkness with no souls. The humans that started to build a society learned to fight against the creatures with powerful minerals and powers created by the Light Soul. This has helped the humans survive,
and even form a military to fight the creatures. One day he will wake back and help drive back the beasts known as Grimm.
AN: Hey guys! This is my first story so please leave reviews for advice. I hope you enjoyed! I do not know exactly when the next chapter will be up,
but it will be up before the end of July. Unless something unforeseen happens before then.