Nanba Prison is a maximum-security prison and the main setting of the Nanbaka series.
Nanba Prison holds some of the deadliest criminals. Its security is tighter than any other prison in the world, with many guards of different nationalities recruited combined with the latest technology; this gives it the world's highest-level security network, even saying that the famous Alcatraz Federal Penitentiary possessed many flaws in comparison.
It's said that no criminal has ever successfully escaped; however, according to the Warden, Momoko Hyakushiki, only one person has escaped thus far: Rokudo, Jyugo's father, known as The Eternal Fugitive and the shame of Nanba Prison.
Nanba Prison is on a remote island floating on the sea somewhere in Japan. There are 15 different areas including the 13 buildings, a general reception area, and the headquarters. The headquarters is located in the center of the building. There are recreational centers such as an arena, shopping mall, movie theater, etc. for guards. The criminals are sorted by crime, trait and abilities, and then sorted to the building with the supervisor best dealing with them. The buildings provide education, knowledge, culture, and manners for the inmates for when they return to society and live on their own. There are unique characteristics to each building: Building 3 is in charge of "education", Building 4 is in charge of "culture", and Building 5 is the pinnacle of discipline and strength and holds a lot of combative type criminals.