Demon Realm

The Demon Realm or Demon World (魔界 Makai), also called Netherworld and Dark Side, is an alternate dimension where the demons ruled by the Dark Lord reside. It is able to corrupt the souls contained within it and is also where Dracula's soul is sent to whenever he is destroyed.Dengeki PlayStation Koji Igarashi interview.
The Demon Realm was first mentioned to exist on Castlevania III: Dracula's Curseʼs Japanese instruction booklet.Castlevania III: Dracula's Curse Japanese instruction booklet story. There it is said that Dracula could summon demons from this place with the assistance of a false god. The Japanese booklet for Castlevania: The Adventure also mentions an "other world" where Dracula summoned his demons from, this time by himself and already being the Demon King.Castlevania: The Adventure Japanese instruction booklet story. It is likely that this "other world" is the same Demon Realm mentioned on the Castlevania III's Japanese booklet.
The Demon Realm was dubbed "Netherworld" in the English localization of Symphony of the Night under Galamoth's description. There it is revealed that Galamoth seeks to take over the throne of this dimension in a 10,000 years plan.Galamoth's Japanese description in Symphony of the Night: "一万年計画で魔界の王の座を狙う魔神" Interestingly and non-canonically, Galamoth does succeed on his plan in Kid Dracula but is ultimately defeated by Kid Dracula.Akumajō Special: Boku Dracula-kun Japanese instruction booklet story.
On the English localization for Dawn of Sorrow this place was referred to as the "Dark Side". Celia Fortner has the power to open gates to the Demon Realm and, with this ability, she is able to make her demons invincible unless Soma Cruz can use Magic Seals. By opening a portal to the Demon Realm she plans to turn her castle into a Demon Castle such as Dracula's Castle. She also says that the power of the Demon Realm is growing weaker and that a new Dark Lord must be crowned post haste, implying that the lack of a Dark Lord may be the cause for the darkness' weakening.Dawn of Sorrow's Japanese script translation at GameFAQs by Rahenna. It is possible the Abyss is simply another name for the Demon Realm, as the portal leading to the Abyss in the castle's basement is referred to as one leading to the Dark Side. 
==References==
Category:Alternate Realms
Category:Storyline Elements