Suderu Koiwa was a normal high school student dealing with the routine day to day life. Until he was shot in the face during a school shooting. He found him self talking to an angel girl. "Tomorrow you will participate with others choose in the ceremony." The next morning he woke up to find everything was back to normal.
The following night right at midnight he found him self being attacked by a monster. The girl angel reappeared before Suderu once again to protect him.
Suderu is dead but to be refreshed back to life he needs to fight the monsters , "Haikaisuru Mono (the other players)," and survive for 30 days.
Suderu's day life has now became a severe survival game. Thus the "Zodiac Game" has started.