An abnormal Red Moon has caused millions of people to collapse.
Upon waking, all of Japan is sealed within the bubble of the Sakkaku System-a partial rewrite of reality controlled by Erisvelle, an ancient entity whose sole purpose is to watch humanity break. Each inhabitant is assigned a Class:

Inspector, Hunter, Lambda, Parasyte... or Lunatic. The latent Yūgen awakens, granting them tailor-made skills and Ultimate Weapons. Parasytes must kill to survive.

The rules change without warning. Betrayals multiply. And when the Red Moon appears, the madness intensifies. Natsuki Tanaka, a skeptical high school student in the astronomy club, still believed in logic.

He will soon discover that in the Sakkaku World, hope itself is merely an illusion designed to make the fall sweeter. A killing game on a national scale.

Where geniuses become monsters. And where even the will to survive can be the ultimate plaything of the game master.