Third Pov
Asta was born without magic but he never gave up trying, but when he didn´t receive a grimoire and his rival told him it was impossible to catch up to him, something inside him broke. He ran into the forest to be alone for a bit and after some alone time he resolved himself to continue trying and not give up. His determination paid of as he got a grimoire after receiving a one-sided beat down from the thief that wanted to sell Yuno´s four-leafed grimoire and his chain. He didn´t care for what attribute it had, how many leaf's it had or how it was even possible for him to have one, he was far to exited for getting one as well as far too angry with the former magic knight to care. After grabbing the giant, rusty and heavy sword he rushed at the now scared thug, his sword cut through the chains like they weren´t there until finally he hit him with the dull edge. After getting hit just once he didn´t get up anymore.
Asta was walking back to the church with Yuno when suddenly their surroundings changed, where once where trees, walls and greenery were now just ravines and craters. It was like a battle had taken place here just a moment ago, another strange thing was his grimoire, not only was it floating in front of him but had also changed its appearance. It was no longer an old rust brown book with a hard to spot clover but a pitch-black book with red veins with no clover. After a moment of confusion and panic he checked his grimoire, or better said the only page inside it. After summoning the sword again, he immediately noticed a change, the once rusty and dull sword now looked just like his grimoire, black with red veins, it even felt different but he couldn´t tell what so he just ignored it.
Time passed, he had long forgotten what happened back then and was now participating in the magic knight entrance test. Asta still sucked in all categories except for one, all the anti-birds didn´t come close to him, this behavior puzzled the captains, they could all feel that he didn´t had an ounce of mana and that the birds looked like the were terrified. All the captains were now paying attention to Asta, especially the captain of Golden Dawn, he sensed something familiar from him, something he had always feel no matter where he was, The World Tree.
Asta was soon challenged by Sekke who didn´t seem to like that he didn´t get that attention. What followed couldn´t even be called a fight, once Asta took out his sword all the captain couldn't help but widen their eyes. The moment he took it, out all powerful being could feel how not only the mana in the vicinity disappeared but how their own seemed to want to hide inside their body. This was something they have never heard about, at this point all of them no longer cared about him not having any mana but started to think about how to put him to use inside their squad, but after some careful consideration they realized that his ability, while powerful alone, was a hindrance to everyone in the same team as him.
Once it was time for Asta´s turn to be selected, unlike everyone else who thought he had no mana and was this useless and wouldn´t be selected, every captain recognized his potential but were afraid he would affect his comrades, after a long silence one hand was raised. Everyone looked the man to who this hand belonged, it was Yami, captain of the Black Bulls.
After he joined the Black Bulls and made some friends, nothing of importance happened until he arrived in the Witches Forest. After getting shot through the heart and reanimated under the Witch Queen´s control he started to transform. The clouds stared to get darker until they started shooting black-red lightnings and setting the forest on fire with black flames, black liquid started to flow from the sword up Asta´s arm and spread until he was completely covered. Once he was fully enveloped, the liquid started to grow into a big ball, after a few seconds the ball started to shrink again but this time some thing emerged that wasn´t Asta. It was a lot taller, had a black armor with red veins.
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Ladros was starting to get afraid and shoot magic bullets at 'Asta' only to despair when they grew smaller the closer they came to their target until they disappeared. 'Asta' didn´t wait any longer and rushed at Ladros with a speed he could barely follow, he just barely dodged by jumping up, but to his horror he noticed that his reinforcement was also getting weaker the closer he got to this thing. He unwillingly had to admit that he wasn´t a match and decided to prioritize his life and run but he didn't go far as the creature reached out its hand and the sword flew in his hand. Once it firmly grasped the handle, it threw it at Ladros and pinned him to a tree, while the injury wasn't life-threatening, it did prevent him from using any magic. 'Asta' turned away from him and looked somewhere in the air, far away the Witch Queen started to shudder as she saw the creature look straight at her through her scrying spell. She had lost control of Asta the moment his transformation started and had no choice but to simply watch, while doing so she noticed that magic lost any meaning near him so she didn´t even think about trying capturing and controlling him again.
The creature looked away after a few moments and started to … melt. From underneath the liquid Asta´s form started to appear again, the moment the liquid completely retreated back into the sword he fell over unconscious. His friends caught his body and looked at the sword cautiously.
First Pov
I had just awoken. I didn´t have the time yet to analyze what happened or changed as I had accidentally taken over Asta´s body the moment I woke up but now I was done I had enough time. The first thing I noticed was that my v.e. had corrupted the grimoire and the sword, due to corruptive nature it got from negative mana, and given them a very small part of its power as I didn´t intention to corrupt it. The next thing I noticed was that I didn´t have my body and was in my soul form, I was surprise that the universe didn´t just continued to move without me being conscious to stay anchored but that might be explainable by the next things I noticed. My Soul looked different, its usual black like the Nothingness had somehow turned into black like the Nothingness with red veins or cracks. It shouldn´t even be possible but here I was, I guessed that my soul had somehow evolved after devouring the anti-soul. In fact, I could feel that the soul was so unique that I wasn´t able to absorb it perfectly and it had somewhat slightly changed my core, I didn´t notice anything at the moment but it was possible that my personality was influenced. Another thing I noticed was that my v.e. has gained a significant boost in quality but sadly not quantity, it has seriously become hard to increase my energy reserve with just absorbing weak souls.
Time passed before I was finally able to find the most hidden but significant change, I have gained a dimension, I was now a 4 dimensional being.
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A/N- Every time I read a ff with absolutely OP MC, I question how he is still a 3th dimensional being, so I made mine a 4th dimensional one. Of course, that isn´t just for fun but has a deeper meaning.