A dystopia where pure females have drastically decreased due to the Apollo drug disaster 80 years ago, putting human survival at risk. In this world, due to genetic abnormalities, congenital "Andromorphs" (commonly known as Morphs) were born, possessing male bodies but also complete uteri and ovaries in place of females, though they require reproductive maintenance. They are a minority and lead social daily lives, but are forced to undergo periodic checkups and are managed by the government.

In this prison, the "National Life Management Bureau Direct Control 4th Rehabilitation Center (Commonly known as: The Nest)," special rules are adopted. Currently, there is a social trend forcing Morphs to marry due to the population collapse, but criminals find it difficult to find matches after release. Therefore, a system called the "Special Marriage Program" exists, where a sentence is significantly waived on the premise of marriage if a romance is established with a guard during the prison stay.