The Ikusaban system was a sociopolitical system created by Mukuro Ikusaba following the death of Junko Enoshima at Hope's Peak at the hands of the Red Army. As vast swaths of territory were still under Imperium control, she set out to purge the planet of hope with nuclear fire to bring about the fabled Despair-Endsieg and to establish a superior race of superhuman post-hopist pure doomerites by the natural selection that the extremely harsh conditions following would inevitably lead to.

Campaigns where entire cities and stretches of land were gassed had been around since the mid-Junkosreich era but was intensified towards the end, especially with the military and logistics factions vying for control by trying to gas as much land and people as possible. No actual nuclear weapons were used until after Junko's death, and only three were ever launched; however, the result of a year of intense chemical warfare and artillery barrages was that a large chunk (approximately 13%) of Western Europe, North America, and a portion of Eastern Europe was rendered uninhabitable.

The Ikusaban system also involved a theoretical warrior race that would be instilled with loyalty by being brought up in the harsh conditions of Todesstädte, or Death Cities, and have superior fighting skill, while being additionally free from hope. High-level imperium officials believed that these warriors would be able to serve their purposes, the remaining population could safely be cleansed with advanced nuclear weaponry.

One point that the Imperium leadership failed to consider was that everybody would have fucking died.