Most of the contents of the book are currently unknown, except for a fragment that serves as the introduction for the book:
A long time ago, King Zahard came into the uncivilised Tower and taught the inhabitants civilisation and ruled over them. He had said, "This place is too boggy".
For us, who were born and raised inside the Tower, it is a statement that makes no sense. But for the people outside the Tower, the "Irregulars", it is something they know very well. Surprisingly, there's no shinsu in their world and something called "air" fills their world instead. They said that the Tower filled with shinsu is too boggy and uncomfortable for them.
I have never seen air, but I have found out some commonalities and differences between air and shinsu by interviewing the Irregulars.
First, the common point is that they both let beings breathe. And they both flow constantly. It is also identical that they are powerful enough to threaten others when they flow harshly.
Then the difference? The biggest difference is indeed the characteristics by the concentration. In shinsu's case, it's more like a gas when it's in low concentration and more like liquid when it's in high concentration. But it seems air is not liquefied even in high concentrations.
The second difference is the circulation. The circulation of shinsu is very fluent but there is no common law. (And the movements are all different by the Floors of the Tower.) But it is said that there are set laws in the circulation of air. (I want to study some more about the laws, but the research is slow because none of the Irregulars that I have met is knowledgeable enough about the laws of air.)
The third difference is consumption. Shinsu exists everywhere inside the Tower. So shinsu exists even in a room that is completely sealed. Shinsu does not flow in from somewhere else, but is rather created from the Tower. So, we can live in the sealed places. Air is not created from sealed places and if a being is locked inside a sealed room, the being will consume all of the air and die. (It seems very uncomfortable.)
You readers may not understand why I, who is not even a Wave Controller, am writing about shinsu on the front pages of a book about weapons. But it is because you are ignorant of the weapons of the Tower. Shinsu and the weapons of the Towers are interrelated. You cannot fully understand the weapons unless you understand shinsu.
All of the weapons we use are modelled after the weapons from the outside of the Tower, which Zahard and the 10 Family Heads brought in with them when they came inside the Tower. Their weapons were, of course, all made to suit air, not shinsu. (Even though some were used in a vacuum.) They had to develop and modify their weapons to suit the properties of shinsu. That's how the weapons we use were born. So it's essential to know about shinsu to understand the weapons of the Tower.
For this reason, there're going to be a lot of stories about shinsu in the following chapters and I request that readers place special emphasis on the relationship between the weapons and shinsu while reading.