Backstory

According to Narcissa, Narcissa, Mary(my biological mother), Regulus Black and Elder Olivander were apparently friends in Hogwarts. Lucius was long ago a graduate. Since they were from an ancient family they knew about the dark lord. Walburga forced Regulus to join death eater rank. And, everyone knew sooner or later they had to join Voldemort. But, they didn't want to. They were weak so they decided to go undercover. And, the rest is history.

Apparently, Malfoy blood is good for light magic. I didn't know that. I always thought they were dark. But, I found, Malfoy's have talent in light. I was dumbfounded. In every generation, Malfoy's gives birth to 2 children. One will be light and one will be dark. Lucius was dark while my mother was light. Actually, they used a ritual to convert light to dark, and Lucius was chosen to be dark.

When the war was in prime, Voldemort and his high-ranking followers got a prophecy. That, someone, will butcher all the death eaters. And, the is related to the light death eater. It was Mary. Lucius didn't want to kill his sister. So, he asked Voldemort to convert the light magic to dark magic. Which, Voldemort was happy to try. He didn't want his right hand to leave him.

So, Voldemort used dark magic to corrode magic in Mary. Since Mary was already adult, the dark magic had a negative impact. Regulus being from the most ancient and most powerful family of Black found a way to save his friend. It was to have a child with pure light magic and have the black magic transfer to the child. Everyone loved the idea. They didn't have any feelings for the child who wasn't even born.

Since Regulus was from the Black family, he was dark magic oriented. So, Elder Olivander was the choice. Apparently, Mary and Elder had a child. And, Regulus used a ritual to transfer the dark magic in Mary to Child. Once the transfer is complete, Mary will live but the child will be aborted. But, they underestimated the dark lord. They found, even if they transfer all black magic to the child, Mary would die.

They loathed themselves. They hated themselves that they tried to use an innocent child to save themselves. So, Regulus used a ritual to transfer his blood to me to control dark magic. While Mary used her remaining Power to give me light magic. Olivander was protecting them. Because Mary was weak, light magic in me was not balanced. That's why I had a dark magic aura when I reincarnated here.

But the system helped me balance it. As for the other story, Olivander died protecting us. And, Regulus had to get Slytherin's Locket so he ran away. He knew Dumbledore no matter what would never kill a child. As for rest, you guys know it all.

As for me replacing the soul, Eve said, because of light and dark magic fighting, the soul never formed. So, God put me inside the child's body. So, technically there is no replacing or fusion of the soul. I was happy that I didn't kill anyone.