From the back of the book:
The red moon rising in the broken world, that is the beginning of the fight.
Together with the red moon, the gate to another world opens.
The third bullet of the present day fantasy RPG presented by Takeshi Kikuchi makes its grand appearance!
The stage for the game is Far The Earth, a world very similar to present day earth. Unknown to the people, this world is being invaded by the "invading demons (emulators)", inhabitants of another world. They are fearsome enemies, against whom normal weapons are virtually useless. But there is still hope left for the world. The name of that hope is "wizards", persons fighting with the lost power of magic.
You become "wizards", and challenge the invading demons in order to defend the world.
The disintegrating world, the four knights of the end, arrive.
The "world kekkai" protecting the earth from the invading demons. But because of the layers upon layers of invasions by the invading demons, the "world kekkai" has weakened. The "four knights" of the end appear in order to infringe on the world and destroy it. In order to resist them with their great power, the wizards have to grow stronger and concentrate their powers. Now, the power of new wizards - you are needed!