
For the last 55 years the Yakuza have controlled everything. But even before then their power was immeasurable. The great series of world wars that shook the nation essentially destroyed all branches of government and the world became a barren radioactive wasteland, mainly for powerful gangs to skirmish for power. The vicious Tensei clan proved victorious not only among other yakuza factions but eventually over the world's criminal empire, and with no government or law to keep them in check, they took control of the population. They essentially are the government from hell, and on the Island of Izayoi the rule with an iron fist and casually torment the inhabitants.

Radioactive war had a vicious side effect. Human mutations. After the first 10 years of nuclear fallout, ghastly looking humanoids were seen roaming the lands, at first they would simply run and scream until passing out, but then eventually they would attack humans. Seemingly at random. Over time a few were seen setting traps for passerby civilians, and also seen wielding weapons. It came to be know that there were 3 strains of mutants. There are the Sprinters who are feral and hyper aggresive, who will chase and tear the skin off any human they can find, but act with no intelligence whatsoever. Then there are the Stalkers who act a little more like primitive hunters, they hide in waiting, and use crude tools to fight and set traps fro humans. And finally soldiers fully intelligent mutants that use modern weapons and military tactics, but they have no society, no order, only killing humans.

Before the world governments were eradicated they activated the 'Offence Network' which was a sentient program which took control of military hardware and controlled them as 'drones' to eliminate hostile forces. The problem was when there is no longer specific nations or factions to invade or defend, the A.I. decided to see all living things as the enemy and simply destroyed any civilization it could find. The Rogue A.I. is usually seen as drone tanks patrolling large wastelands killing animals and mutants wherever they may roam. Humans have long learned to not engage with the A.I. if possible, but every now and then, a very destructive encounter will happen.