Tokyo (東京) is the primary setting for the Coppelion series. Due to an earthquake 20 years ago, a meltdown occurred at the Daiba Nuclear Power Plant leading 90% of the population of Tokyo to be dead. People who evacuated from here mainly went to Osaka or Nagoya.
Tokyo is commonly known as "city of death" or "ghost town" because it is filled with radiation.
The governments usually drop emergency supplies since the nuclear powerplant incident, but stopped 15 years after that because they believe that there are no longer any survivors.
20 years after the nuclear powerplant incident, the governments send the Coppelion units into Tokyo to carry their assigned missions.