Demon Lord's Reincarnation

Erste had given the Old God true death as he not only destroyed his body but his soul, the energy of chaos even eroded some of the rules that the Old God controlled. Despite giving him true death some of the Old God's power was devoured by Erste. Still, at the moment Erste didn't even feel the power he had gained as he was in a state of euphoria after having such an incredible battle. 

This battle was something he could never have imagined, not even in his wildest dreams could he have seen himself slashing through someone bigger than several planets. Now that he had a taste for it he wanted more, he wanted to battle more.

Even as he was bleeding all over inside and out, and had several broken bones that didn't stop him from relishing in the excitement of the battle.

...

The ORIGIN who was watching hidden from everyone's view felt something new for the first time in eternity. The ORIGIN who knows all from what has been and what could be, the ORIGIN who has seen all the dimensions, parallel universes, multiple multiverses, the omniverse, and even beyond that to the void were he lives was actually surprised. 

On most timelines and even parallel universes Erste would die in this battle there were some versions were he would be able to flee with Gratz and die due to his injuries, but there were never any versions of this battle that he would actually win. 

This time not only did Erste win but he was able to tap into the chaos energy within the void, that's a place beyond the omniverse the ORIGIN created, the void was a place that existed even before the ORIGIN itself.

The ORIGIN who had breathed in chaos energy since the ORIGIN existed was able to control and manipulate it at such a high level that the ORIGIN was able to use chaos energy to create. Even though Erste was able to use chaos energy his use of it was extremely crude. 

Still, it was an amazing feat as the ORIGIN had tried numerous times to create a creature that could use chaos energy but despite trying different things the ORIGIN was unable to do so. In the end, the ORIGIN was forced to create a pale imitation of chaos energy which was the mana used by Gods. Yet now aside from him, the ORIGIN finally found another who could use chaos energy and had the potential to create his own omnniverse. 

"Am I finally no longer alone?" 

Erste was now the first creation the ORIGIN made that was outside his control, not only that but every single being that had contact with Erste had become a blur in the flow of fate. Erste who had disappeared completely from the flow of fate and the people surrounding him who had become vague existences in the flow, the ORIGIN was getting excited to see what they would do. 

...

After defeating the Old God and reveling in the afterglow of victory Erste fainted, by the time he woke up he was already on a bed in an unfamiliar room. Erste tried to stand up but he could not move, it was at this point he felt extremely weak and sleepy. When Erste tried to circulate his mana he found that it was now flowing properly. 

"You're awake!" 

A nurse entered the room and shouted as she quickly went out and called a doctor. 

...

Erste who finished talking with the doctor learned that he was actually asleep for an entire year. When he was brought to the hospital back in the rebellion's dimension, Erste was in a very bad state. The doctors who had seen him used various tools to check on his body and what they saw was surprising. There was some sort of unknown energy stopping his body from trying to heal itself, if this kept on going Erste would really die. Seeing such a rampant unknown energy something that they had never seen before, the group of doctors needed time to study it but even then they knew it would be difficult to heal him even with the power of mana and technology. 

When they had given up on saving Erste and decided to study his corpse something incredible happened. The unknown energy that was destroying his body just disappeared and the moment it did so, Erste's body returned to a normal state. Only then were the doctors able to heal his body. 

...

'Unkonwn energy... Was it that energy I felt?'

Erste tried to see if he could once again use the unknown energy he used when he fought the Old God, but try as he might he could no longer sense it. Still, Erste did not give up as he continued trying to sense that unknown energy, while he was doing that someone had entered the room. The person who entered was a familiar face, he was the last person Erste was with before he fell into a coma. 

"Hello, Gratz."

"It's a pleasure to see you awake, Erste." 

"Hoh, no longer calling me boy are you?" 

"I apologize for misjudging you, Erste." 

"Boring, that should mean you won't play with me anymore." 

"If by play you mean have a match then you don't have to worry I would gladly spar with you if you want, but as someone who can defeat an Old God I don't think I'm worth the time." 

"But I think in my current state you can prove to quite the challenge." Erste smiled as he tried to raise his hand. 

"That it might." 

"So what happened after I fainted?" 

"After you fainted, I woke up and saw you on the ground while the entire dimension was breaking apart. It was the first time I saw something like that, it was an incredible sight watching an entire dimension break like that. I picked you up and fled back here, and the doctor should have already told you what happened afterward." 

"Yeah..." 

"Erste, thank you for protecting me." Gratz bowed his head. 

"There's no need for that, you saved me from the collapsing dimension, so we're even." 

"Even so, I still want to thank you..." 

"Fine, you're welcome then." The two looked at each other for a while and both had smiles on their faces.