The Realm of the Dead is a location in the Kishin Douji Zenki series.
The Realm of the Dead and its other names
Notably the name of the location greatly differs depending on the character mentioning it.
In Episode 27 of the anime, Roh calls the Realm of the Dead "Rerumu shisha no". "Rerumu" (レルム) is nothing other than him using the English word "realm" as a loanword. This occurs in the Japanese audio, when Roh introduces himself and mentions his father Engai.
The singers in the background music of the actual Realm of the Dead refer to it as "O-shini-mouke"
(おしにもうけ) instead, which is pronounced as O-shini-moke and accurately translates as "the sky" or "heaven".
Some of the anime dubs and subs falsely refer to the Realm of the Dead as the world of death.
Engai and the Inugami Roh
Being the son of Engai, a character that is only mentioned by name and never seen in the actual series, Roh is the prince of the Realm of the Dead, though due to Roh being expelled to our world, Kagetora tries to claim the title of the king of the Realm of the Dead in Roh's stead. Being a vicious man, Kagetora wants to reap this title by force, even going as far as abducting Kokutei and turning him into a world ending beast, though Kagetora's victory doesn't last, as the transformed Kokutei swiftly dispatches the new "king".