Gantz (ガンツ, Gantsu?) is a Japanese manga and anime series written and illustrated by Hiroya Oku. Gantz tells the story of Kei Kurono and his friend Masaru Kato who die in a train accident and become part of a semi-posthumous “game” in which they and several other recently deceased people are forced to hunt down and kill aliens armed with a handful of futuristic items of equipment and weaponry.
After the non nuclear war wipes out much of the major civilizations in the world, chaos takes over. But a heaven on earth has been realized and that heaven must be protected form constant threat of terrorist attack. That place is called Olympus and Its protection lies in the trust of the ES.W.A.T. – an elite group of individuals sent out on missions to protect Olympus form outside threats before the threats become severe. When they are sent out on a mission to thwart a group of Cyborg Terrorist, they loftily stumble upon a political plot that threatens the ideals of the city-state Olympus.