(Synopsis from the back cover):
«“May your courage save your world.” The Monarch of Destruction and the armies of Chaos have descended upon Earth, leaving nothing but death and carnage in their wake. The fate of humanity lies in the hands of the newly crowned Shadow Monarch, Jinwoo Sung. Who will be the final victor when the dust settles on this timeless feud? And more importantly, will there be anything left of the world to save?»
Basically, the final battle takes up five fairly short chapters, and the remaining two-thirds of the book consist of "bonus stories." That is, the main plot ends relatively quickly; everything else is additional tale. However, these stories are quite interesting. Even though the main plot has concluded, they offer new perspectives on various scenes and characters. Furthermore, they're called "bonus stories," but they actually function as a continuation of the story. They're worthwhile and are canonical, meaning they're officially part of the plot.
There's a character who's a medium, a fortune teller, a clairvoyant. Then, a police officer and crime investigator punishes a criminal and, you could say, tortures him endlessly. There's also a girl who commits suicide, and the method of suicide is detailed; I suppose it might give some ideas.
I can say that after eight volumes of novels and two seasons of anime, you grow quite fond of the characters, and the bonus stories and the epilogue are a tribute to all those secondary characters who have accompanied Jinwoo throughout this journey. And the ending, the epilogue, is exciting.