After the MC of the book left the Holy church, he wandered around the world in search for meaning to his existence.
As a man without a home or family, he had essentially become a scholar.
His only hunger was for knowledge, and a better meaning to life.
He met a variety of people, and engaged in different cultures.
One of such was a small tribe that lived in one of the most dangerous parts of the world.
Their entire tribe was surrounded by a special cardinal point where cored beasts were as much as ants in a colony.
Survival was the catalyst for innovation.
They used ancient runic symbols to channel the power of beast cores into their own bodies.
This made them nearly invincible to attacks.
Of course, the ritual had very rigid requirements.
For example, the proximity to the ritual site was one of them.
Straying too far would render the process useless.
There were others, like the kind of beast to use.
Each beast a distant cousin of the other.