Backstory- Bakuto's backstory is a bit vague as he doesn't remember details. Such as names, or dates just and hear say of how things happened.

Bakuto was born the clover capital within a noble house. He wasn't born a noble, he was born of a child of a servant. Or at least that is what the nobles called his family, in reality they were just their slaves. When the eldest child of the noble family was to get their grimoire, to their disgust it wasn't their child that got it but Bakuto instead that got chosen.
A book as hard as a rock, more or less condense ash made stone choose Bakuto to be its wielder. In this book was a bound spirit. A mighty phoenix spirit, a beast of fire. The noble family was furious. The patriarch of the family on the same day Bakuto got his book beat him to death and tried to take the book and give it to his son instead.
The Curse of the book activated the moment it choice Bakuto as its owner. Moments after Bakuto was beaten into a bloodied corpse his body burst into flames. Setting a few of the nobles' positions on fire as Bakuto came back to life. Bakuto was fifteen when he first died and came back looking like he was ten again. The book however the spirit in the book is a very unhappy being. So when the other child took Bakuto's the spirit lashed out and turned them to ash.
This added Bakutos slavery to whole other levels of despair. While the Patriarch was furious and mourning over the loss of his own son and that killed Bakuto was obviously not happy he wasn't still dead. This cruel man found a silver lining in this and it was Bakuto's magic. He wanted Bakuto's magic for himself. He wanted the ability to come back to life after death. Bakuto was subjected to endless torture and repeated deaths for fifteen more years after he got his grimoire for the first time.
This family fled the Clover Kingdom to 'study' Bakuto believing they could harness his magic and make themselves stronger. He was even planning a coup to take the capital at one point. The magic knights stopped them when they were away from home. It wasn't months later they learned about the Bakuto they held as their slave now guinea pig for cruel experimentations.
When they found Bakuto they sent him to an orphanage. A senior knight at the time was trying to figure out how Bakuto was even alive, because they found him chained without food or water months after the Nobleman who had him was taken down. Seeing a grimoire the knight told the boy who appeared to be ten years old at the time that once he grows up join the magic knights.
Bakuto after all he went through he barely remembers any of the trauma he has been through though. Dying on repeat sort of 'scrambled' his brain. Whether it be from the flame spirit burning his body or his mind just blocking out all the details. He does have memories and on occasion is filled with hatred but he doesn't dwell on the bad past.
One moment when he was rescued. He remembers the magic knights and knowing he wanted to be like them to save people from things has been through.
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So days in the orphanage lasted three days before Bakuto ran away to live in the woods to look after himself. He spent himself training on his own every day. Physical training. Mental training. .
Bakuto left them saying "I can't stay here,' I gotta become a magic knight yesterday. Gotta go!" He spent years on his own training. Learning spells. Honing his skills. Dying a few more times because he picked fights with wildlife. Then relearning new spells again after dying. Bakuto spent a bit of time fighting in the forest until he defeated most of the biggest creatures in the little remote forest he found himself in.
He made his way to the cities and towns where he was teaching himself the ways. Breaking into libraries, churches and what not so he can learn and read. Spent time in jail, on five different occasions. Until he turned seventeen, or at least made it to the age of seventeen. this time around. Once he figured he was ready he made his way back to do the exam to become a magic knight

Back Story Summary- Bakuto was a slave who got a grimoire, was murdered, came back, tortured, and rescued. Trained himself in forest training fighting monsters and beasts. He turned seventeen, but he died enough times. While his current life is up to seventeen but his actual age he is seventy years old. Now he believes he is ready to become a magic knight!