Two baby boys are left outside the church in Hage village. Father Orsi would take them in. When Father Orsi took a good look at them. He would he see that one's name is Yuno since it is written on his clothes.He had a pendant on him. Yuno was sound asleep. Father Orsi turned his attention to the other child. He had the name Asta written on his clothes. Asta had a smirk on his face. The smirk on his face was not that of a child that happy. But a mischievous one.
Timeskip 5 years
As Asta grew up he didn't act like a child. He acted like a adult. He regained his memories of previous life(as Aizen) at the age of 4. Asta considered going back to his evil ways but decided against it. He had a family now. He decided he would protect them.
In the world he was currently was in people used magic. He was the only one who did not possess magic. There were no Soul Reapers or Hollows. He concluded that this a alternate world where the beings of his old world did not exist.
Back to story
One day Father Orsi gave Yuno a letter. He told him to deliver it to the next over. Father Orsi told him he could ask Asta to go with him. Orsi told he could ask Asta to go with him. Yuno refused because he didn't want to bother Asta. He viewed Asta as a big brother who always took care of him. He felt like he was a burden to Asta. He wanted to do this on his own. Asta would decide to follow him.
Yuno would make his way to deliver the letter. After delivering it on his way back to the church a drunk man would snatch his pendant. He would kick Yuno to the ground. Yuno asks the man to give it back. He refuses and decides to leave. Just about when he was about to walk away Asta appeared behind him and broke his leg with a strong kick.
"Argh my leg" the drunk man
"I should thank you for taking care of my little brother. How about I repay you by breaking your other leg." Asta said with a smile.
The man started get afraid.
Asta walked towards the man. Just when he was about to break the man's other leg Yuno stopped him.
"Asta stop please."Yuno begged Asta with tears in his eyes
"Okay fine." Asta said before going to get Yuno's pendant from the man.
"Here. Make sure not to lose it again. Well let's go home." Asta said as started walking
Yuno followed after him.
"Asta do you think I could become strong like you. " Yuno
"Yes you can if you decide to train hard and stop being a crybaby. " Asta
"Okay. From now on I won't be a crybaby and I will surpass you and become the Wizard King." Yuno
"Surpass me huh. Well then I look forward to seeing you become the Wizard King." Asta said as he ruffled Yuno's hair.
Timeskip
Asta would decide to master all of his abilities from his previous life. He would find a isolated place and train from the age of 7. After training for 5 years. He decided he would explore the world. He would leave a letter for his family explaining his reasons for his departure. On his travels he would visit the Diamond Kingdom, Heart Kingdom and infiltrate the Spade Kingdom. He would learn of the races of the world( Devils,Elves, Dwarves and Humans). The cultures and kingdoms histories, etc.
After traveling for 2 years he went back home.
Asta arrived to see Yuno training and the rest of his siblings watching Yuno train. They ran towards when him when they saw him.
"Asta you are back" Said Recca
"Yes I am." Asta said as he picked her up and hugged her
Asta put her down after he hugged her.
"What's with the getup." Nash said referring to Asta's clothes

"It is the uniform of the organization I joined." Asta
"The organization I betrayed"Asta thought
"Fight me Asta." Yuno suddenly said
"Maybe later." Asta said before going inside the church
When he gets inside the church he greets sister Lilly and Father Orsi. They were happy to see Asta was back home.
One year later
The year went by with Asta spoiling his family with the money he earned from his travels. Yuno constantly challenging him to fights which he refused. Yuno trained his Magic
The day came for Yuno to get his grimoire. Asta tagged along. Asta didn't worry for a grimoire since he did not possess magic. They would go the grimoire tower. The grimoire ceremony begin. Yuno would get a four leaf clover grimoire. Upon getting his grimoire Yuno declares that he will become the Wizard King. Nobles would get angry at Yuno's words. After Yuno said those words he placed his grimoire in a holster. He and after leaveafter that. On their way home they are stopped by nobles. These nobles were mad at Yuno a commoner for getting a four leaf clover grimoire while they didn't. The two nobles summoned their grimoires they just gotten and prepared to use spells.
Yuno summoned his four leaf grimoire and used a wind attack. He used Towering Tornado.

The attack blasted the nobles away. When the two were blasted away. A chain suddenly made It's way to Yuno. Asta deflects the chain with his sword.
"I was wondering when you would reveal yourself. Even you tried to hide your presence you would still not be able hide from me" Asta
As Asta said that Revchi out from a corner.
"You quite interesting you were able to deflect my chain. I don't sense a drop of mana coming from you."
Well anyway I am here for that boat's four leaf grimoire. Get in my way again and you will die." Revchi
He then told Asta and Yuno not to test him because he was a former magic knight. He then send his chains at Asta and Yuno capturing them both. Yuno found his magic sealed. Revchi then decided to insult Asta.
"You pathetic trash. You think someone like you who does not have magic can beat me." Revchi laughed
"You think you arw better than me just because you have magic." Asta
Yes" Revchi
"How naive. Comparing me to you is like comparing a ant with with the heavens." Asta said before he released his Spiritual pressure.
"What is this pressure. It feels more potent then killing intent." Revchi thought as he stood frozen with fear.
"It looks like I still have a long way to go before I surpass you." Yuno thought
Asta broke out of the chains easily. After getting out of the chains Asta continued releasing his pressure. While he was releasing his pressure a grimoire suddenly appeared in front of him. It was dirty,had a red aura and it had a five leaf marking on grimoire.
"A five leaf clover huh. That means their is a Devil inside the grimoire. Interesting" Asta thought
The grimoire suddenly opened up and out of it came a sword. Asta grabbed it and started walking towards Revchi.
"I hope you prepared to die." Asta said with a smile
"Asta don't kill him." Yuno
"Argh you are no fun."Asta said before appearing before Revchi
He knocked Revchi out. After Revchi became unconscious the chains restraining Yuno were released.
"It looks the future Wizard King needs me protect him."Asta
"I had that covered.''Yuno lied
"Oh sure you did"Asta laughed
"I will become stronger so that you don't need to protect me."Yuno whispered
Asta heard this
"Yuno I will always protect you. It doesn't matter if you become Wizard King or whatever. I will still have your back. " Asta
"I don't need your protection."Yuno
"Well anyway let's give this guy to the Grimoire Tower Master." Asta
Asta and Yuno handed Revchi over to Tower Master. The tower master was surprised to see Asta had a five leaf clover. He gave Asta a warning about his grimoire. Asta simply nodded when he said that.
After that they go home. On their way home they talk about upcoming magic knight exam which would take place in 6 months in the clover kingdom capital.
Both of them would enter the exam. One to start his journey to becoming the Wizard King and the other thinking he it would be fun.
Tbc