Seto has possesion of a mysterious book in a language he can't read. (obviously you guys can read it now, but for the sake of the story the Runic language is a hard to decipher code. Though in real life it isn't)

On the cover of the book (which you've never seen) Is a word written in Runic, if shown, you would all decipher it says Etoriis.

Now before you make any assumptions, Etoriis is the name of a country. I will not hide it as there's nothign secretive about it. Etoriis is the name of the country that Rekrium is in. Rekrium is a small piece of land separated from the rest of the world by a ring of void impossible to cross.

I can tell you all this, the mysterious book titled Etoriis is a history book. It is a record of the entire history of Etoriis from it's creation to now. It technically is still being written.

Anyways the book is VERY important. Like VERY. I can not stress enough that history is KEY to understanding this story.

Some history you'll learn from the book, some from the narrator, some from other characters, most from Adam's visions. 

HISTORY IS IMPORTANT

Concerning the image in the book that Adam has a connection to. Very important. It has a very dark history to it. An important historical event at the root cause of the Rekrium curse and more tragedies not yet revealed.

Adam's death visions is where you'll learn the most of this historic event in the perspectives of those most important to it. 

Their names replaced with virtues or vices to represent them.

That's all on this matter for now. More as the book continues