In Buddhism, "Naraka" is a world where people are sent to in the afterlife. When the concept was adopted to Japan, it is translated as "Naraku" (奈落) and is equivalent to "Jigoku" (地獄), meaning "hell." "Narak," literally "Hell," in Sanskrit, is the domain of the lord of the Dead, Yama, in Hinduism.
An area filled with demons that attempt to enter the rest of the Eastern Kingdom of Mikado or choose to live there willingly, one of the Samurai's duties is to patrol and slay the demons that wander the realm. It is also a training ground for new prentice Samurai and their peers. Alraune creates a Domain on the 3rd Stratum, while Samurai guard the stairs that lead to the 4th Stratum as Samurai code prohibits going to the deepest depths. A legendary demon said to have served King Aquila is mentioned to be keeping Samurai from going further. The demon is revealed to be Minotaur and waits in the Hall of the Minotaur to strike down anyone who tries to proceed.
Naraku is said to lead into the Unclean Ones country. The bottom part of Naraku is in fact the Sky Tower (スカイツリー, Sukaitsurī), with Medusa at the bottom. She prevents everyone in Tokyo from being able to go up the Tower. An Ashura-kai member mentions a leader of a military group who currently hangs out at the Florida Cafe once led a team that dug the tunnel which lead to the surface and into Mikado.
After the gate to the Expanse is opened the path to Mikado is blocked at the gate to the entrance of the Hall of the Minotaur, where the Angels set up Purgatorium to keep intruders out. All demons disappear from the top floors, while only Fallen Angels can be found in the bottom floors. Angels stand guard throughout the top floors. Once the angels are defeated on the Neutral route, it is now filled with demons that reside from the lower floors.
Walter travels with Stan through Naraku in order to reach Tokyo, where they are confronted by the Minotaur. The tower is later destroyed, separating the two lands form each other. Gina is able to return thanks to her light powers while Walter stays in Tokyo.
Nanashi and Asahi initially visit the Sky Tower while respoding to a request for help regarding a hunter who had been captured by angels. The two are at a disadvantage until Flynn and Isabeau arrive to help the hunters.
Later, the hunters must ascent the tower along with Hallelujah and Abe of the Ashura-kai. While ascending the tower, the party encounters a resurrected Medusa, who was revived by the Divine Powers. After her defeat, the party recovers components needed for the Shesha Radar in the excavation site.