|This article is about a/an location in Kamen Rider Black RX.|
It was later revealed that this world is actually a mirror planet called Shadow of the Earth (地球の影 Chikyū no Kage), and it has been almost ruined by the environmental pollution of earthlings.
In the distant past, The Demon World was a peaceful planet filled with people who had Antenna on their head, until the Crisis Emperor arrived and conquered it, turning it into an industrialized universal power which expanded its claws onto multiple planets. However, due to the Emperor's policies, completely disregarding the nature of the Demon World, its environment was destroyed and the planet itself was slowly dying, heading to complete destruction. There are only 30 days in a year where the sun shines upon The Demon World: Two of those times were when Kohtaro Minami was there.
Invasion of Earth
Aiming to save his empire, Crisis sent his army to take over Earth, planning to destroy humanity and move the population of Crisis from their original world to rule Earth.
In one of of their plots to annihilate Kohtaro, Naval Commander Bosgun sent Gynagiskhan to take him to the Desert of Fierce Winds in the Demon World to destroy him. In doing so, he also brought Reiko Shiratori, Shigeru Sahara & his two friends Saburo And Kengo. Reiko was found by a Professor named Wald, who along with his followers were against the emperor. Kotaro found the boys and saved them from Gynagiskhan. They later Met up with Reiko and Wald, who explained the planet's history. Wald then Gave Kotaro a floppy Disc containing the blue prints to Ridoron. Wald was killed by Gynagiskhan, who was then Destroyed by Kotaro. Upon the Monster's destruction, a portal opened up for Kotaro, Reiko and the boys to make it back to Earth.
When Intelligence Staff Officer Maribaron kidnapped Hitomi Sahara to replace and make her look like Princess Garonia, Armored Officer Gatezone sent out Deathgaron to keep Kotaro from interfering. Using his Macro Eyes, Kotaro found that the red button on the left side of the Robot's chest was a way to get to The Demon World. After pressing it they, both made it to the Demon World. During this quest, Kohtaro learned about the Valley of Miracles which has water that can age a person as well as a holy spring which is similar to the fountain of youth. He also gained two new forms for both himself and Acrobatter as well as new weapons and a new friend and ally. , , &
There were three Pieces of a Key which would open up a portal to The Demon World, allowing all the of the Crisis Empire's inhabitants to instantly invade earth. Kotaro met a woman named Youko, who had two of the three pieces. Kotaro reluctantly helped Her to break into a museum to steal the third one. Youko took a picture of a map the three pieces made and headed to the mountains. As she attempted to put the peices in, Gatezone arrived and told her the purpose of the pieces while holding her at Gun Point. Kotaro arrived and saved her, only for Gatezone to summon Elgitron. Kotaro called for Ridoron and they retreated.
Once safe, Yokou told Kotaro that she was once engaged to an American test pilot named Jim, who had encountered the Crisis Fortress during one of his flights and wrote about it in his Journal. After he was killed in another one, a devastated Youko thought it was a malfunction with his plane, until she Found his diary and read about his encounter. Kotaro then realizes it was the fortress. Youko reveals that she and Jim found the first piece on sale by an old Indian Man, while the second one they found by mistake in Australia. They both kept the two pieces as pendants to symbolize their engagement and that his piece reacted to the time-space barrier during his first test flight. Youko also reveals that she gave Gatezone a fake third piece, while she revealed that she had the real one.
When Gatezone and Elgitron arrived, Kotaro transformed into RX as a diversion to let her escape. Unfortunately, Gatezone stopped her by blasting her unconscious and took the real third piece to open up the portal. When Youko awoke and saw what happened, she provided RX with a diversion, allowing him to make the monster fire its weapon on the key, damaging it severely. Unfortunately, the smoke caused Youko to lose site and presumably fall to her death. Maribaron took the damaged key and had a plan of her own. RX Soon destroyed Elgitron.
When Kotaro tried to find Youko, He found Jim's Journal, which made him realize that Youko was alive and nearby. Youko was found by an old man and his Granddaughter Mika, both of which were descendants from the demon world, which the old man thought was A "land of paradise". Maribaron had spied on them and saw that Mika had taken a liking to Youko and impersonated her as a way to get Mika to repair the key and open up the portal. She sent out Ganma to keep Kotaro occupied. When the old man revealed that the people of Okukumo shrine, especially young kids had the power to fix the key, Youko realized what was happening and went to stop it. She was ambushed by the Skullmastars, but RX arrived and stopped them. When Mika saw two Youkos, she was very confused. The real one showed Mika her favorite doll, causing her to walk away from Maribaron's Pillars and cause the entry to The Demon World to begin to disappear. When Maribaron attacked Youkou, Mika saw her doll fall and threw the key down to get it. Maribaron tried to convince her not to, only for Mika to let out an outburst, which gave off an aura that destroyed the key. An angry Maribaron shed her disguise and attempted to kill both, Only for RX to stop her. After failing to kill all three, she called for Ganma to finish them. Ganma was then destroyed Soon afterwards.
Environment Change Failure
The Crisis Empire tried to change Earth's atmosphere to make breathing easier for the invading inhabitants only For Kotaro and Joe to stop them. When a whole bunch of Crisis Citizens arrived, they fell victim to Earth's oxygen and their ships crashed and exploded. Maribaron was supposed to give them enhanced cells that would make them adapt.&
In the last fight against the empire, Black RX finally sees The Demon World itself from space, and realizes that it's identical to Earth. Dasmader claims that The Demon World is a mirror planet to Earth and it's dying due to Earth's pollution and humanity's evil only for Kotaro to reject his claims, affirming that it was the Emperor's policies that led to that.
After being defeated as Dasmader, the general revealed himself as the Crisis Emperor in a last attempt to defeat Kotaro. He was destroyed by RX's Revolcane and The Demon World blew up as it was linked to him. While dying, he claimed that as long as humanity's evil continued to exist, they'd give birth to a new Crisis and he'd return alongside it.
- Crisis Empire
- Citizens of Strange Demon World