Hell (地獄, Jigoku), is the afterlife of evil humans and evil spiritual beings. The gates of hell serve to both allow evil beings to enter hell, and prevent them from escaping. Hell is a spatially infinite plane with numerous domains and realms that occupy it, seperated by the River Styx.
The River Styx
The River Styx is a vast white emptiness that serves to seperate the various realms and domains within Hell. It is spatially infinite with travel between realms dictated by the Peregrine the ferryman of the dead, and the more illusive Charon who often bargains with wayward souls for passage. Both of these entities are the only ones capable of safely traversing the River Styx, along with extending safe passage to others. To anyone else who wanders the River Styx, it possess a terrible power, robbing those within it of their memories, and eventually their will, until they discorporate into nothing.
Elysium is a vast region of grassy plains, forests, and mountains. Most of it is untouched wilderness, and is inhabited by bestia of all types and kinds. Atropus is the capitol city of Elysium, and is the seat of Arthfael Mendax's power and influence. It is a city of bustling and hustling; the majority of deceased and evil liars, lawyers, and politicians reside here.
Malebolge is a swampy, rocky, and inhospitable region ruled by the Optimate known as Beezlebub. Acidic lakes and deep natural caverns pitmark its surface, and at all times swarms of insects and foul odors plague the inhabitants. Evil humans that succumb to bad or wasteful habits, chronic or lethal diseases, and old age end up here. Malebolge has the largest population of imps among Hell's domains.
Ragnarok is a vast volcanic desert, strewn with rusting weapons and collapsed buildings. In its endless battlefields, powerful diabolus conquer the weak and slaughter each other for pleasure and influence. The majority of hollows and evil, violent humans end up here. Amon, the ruler of Ragnarok, controls his servants with force and brutality alone.
Tartarus is an endless maze of underground catacombs, tunnels, and dungeons. Its ruler is Beherit, the Duke of Graves. It is a dark, silent place of contemplation and loneliness. Evil humans that have succumbed to suicide, despair, and self-hatred reside here.
Styx is a strange, roiling veil of chaos that connects the regions of hell. Anyone that passes through this "river" and is subjected to its flow lose his identity; he suffers total amnesia. Because of the vast distances that must be traversed to arrive in another domain, these travellers invariably lose their way and never return. Only Charon, an S-class daemon, is known to have the ability to pass across and navigate the rifts of Styx without being harmed. He sometimes ferries other beings across... provided they can pay his prices.