In a city, buried in filth by its human residents, a cleaning robot gains sentience through tampering. This robot develops a hatred for the city’s putrid state and those who made it that way. The bot came up with a plan to return the world to nature, dubbing itself the “Cleanser” Using the discarded scraps piled throughout the city, the little cleaning bot built on to itself and began building other bots. It stashed its own bots around the city, hiding them in the squalid alleyways and in a hodgepodge ship made of several chunks of old aircrafts. With all in place, the Cleansing began. Humans were exterminated throughout the city in an event known as “The Cleansing.”