The Crisis Empire is a alien group attempting to invade the Earth and exterminate the human race. They claimed that their home planet was being sucked into a black hole. Since they thought that humans didn't really care about the Earth, the Crisis Empire thought it was justified for them to take over. Strange Demon World is the original dimensional world where the great Crisis Empire resided. In a distant peaceful past, the world used to be connected to the Earth through a dimensional portal. But until the rise of the Crisis Emperor, Grand Lord Crisis, the portal were sealed off by the people of Strange Demon World who opposed the rule of the Emperor. The two worlds drifted apart and the past was forgotten. They captured Kotaro and forced him to join their organization but he refused. Therefore, they attempted to kill Kotaro but their plan backfired when Kotaro eventually became a stronger version than before. Thanks to a particle beam that was shot through his stomach, Kotaro was evolved from Kamen Rider Black into Kamen Rider Black RX.
In final battle on board the mother-ship 'Crisis Fortress' with Grand Lord Crisis, the Emperor revealed to RX the truth about Strange Demon World. As the 'Crisis Fortress' travels towards Crisis dimension, the true face of the Strange Demon World is shown - An exact 'mirror' world of Earth itself. Grand Lord Crisis blames the dying of their world as an effect coming from the pollution of Earth's environment by mankind. Professor Walter told Kotaro Minami that the suffering of their world is caused by the evil ways of the Crisis Emperor. In the end of the battle, Grand Lord Crisis claimed that as long as mankind lives on "the pollution they caused", there would always be another Strange Demon World. As the Emperor died by a stab from RX's Revolcane, the Strange Demon World is shown to explode as well.
Grand Lord Crisis is the ruling dictator of the Crisis Empire, who is not seen at first but mentioned several times throughout the series. He resides in Crisis City at the Empire's home world. He eventually offered Black RX the chance to replace General Jark and become the new right hand or even rule the Earth. When refused, he summons his host body Dasmader to finish Black RX. He appears as a giant alien head in the finale after the death of his host body Dasmader. He was destroyed by RX's Revolcane, with his dimension ceasing to exist as a result while claiming his immorality that he will always return as long as evil exists.
General Jark is a military leader of the empire and supreme commander of the invasion army. He carries a long staff that releases yellow electricity. Jark has the loyalty of most under him as he initially leading the attacks until Crisis arrived. He actually does care about his subordinates even to save Maribaron from being killed by Dasmader. Towards the end of the series, he was forcefully transformed by Crisis into a stronger warrior called Jark Midla to kill RX. In the process, Jark Midla easily murdered the Sahara parents and defeated V3 and Riderman while X and Amazon rescued the Sahara children from his grasp. When he was in the middle of battle, the Sahara children tried to kill him but RX as RoboRider shielded the children and transformed into BioRider. He was inevitably killed by RX with the Revolcane after a long battle. Regressed to his normal form and near death, he proclaimed Crisis was too powerful even for RX.
The sorceress of the State from a noble family outside the Crisisians with feelings for Jark. She uses the yellow feather on her helmet as a weapon or to send messages, along with using a laser whip and breathe fire. She cares for her comrades, displaying it when Lord Crisis' living heir Karuoriya dies in a freak accident on their watch and she attempts to cover it up by kidnaping Hitomi to take her place. Though Jark learned the truth, he allows Maribaron to take the girl to the Miraculous Valley to complete her plan. But when Kotaro saves Hitomi, Maribaron is advised by Jark to make a false report that the princess was killed by RX. When Granzyrus arrives, Maribaron revived the spirits of 10 soldiers Kotaro killed to finish off the other riders. She was eventually shocked to learn that Dasmader was Grand Lord Crisis' mobile body. She was killed by Crisis when she objected on his decision to have RX join them.
Bosgun is a Crisisian, who wields a jagged sword and dagger. He is in charge of the Man-Beast/Mutant unit. He once plotted to take over General Jark but his plans were foiled when one of his swords was destroyed by General Jark himself upon discovering his treachery when he lost to RX twice. He died fighting when he was stabbed by the Riboclane Sword during the arrival of Granzyrus.
In charge of Robot unit, he took to fight Black RX occasionally. He is armed with a blaster and a powerful motorcycle. Gatenzawn had the ability to detach his own head from his body. His body could still move on its own without his head. In his final episode, he died fighting Black RX while attempting a suicide bomb (With his head separated from his body) attack, with only his head remaining before it was shattered by his own laser beams reflected by Black RX.
A small, unusual creature who owed his life to Jark and is one of his most loyal minions. He is constantly jumping around and annoying everyone else. He is the most cowardly and is quick to ditch a battle before it's even over. He was soon targeted by Dasmader, Gatezawn and Bosgun when Grand Lord Crisis was about to destroy them all, but he soon gave his life to ensure the others avoid Crisis' wrath when he transferred his life energy into Gedolridol before his monster died at Black RX's hands.
Sent by Crisis, Colonel Dasmader is an inspector whose task is to put the invasion party back on track, receiving utter contempt by his peers due to his arrogance. Dasmader could fire a green laser, with a shape of a dragon's head from his helmet for combat. He was almost killed by both General Jark and Black RX. He later leads Gatezawn and Bosgun in the attempt to kill Gedorian to appease Crisis' anger. Dasmader was stabbed in the back by Jak Shougun when Jak was trying to save Maribaron from being killed by him. RX successfully threw his Revolcane into his body and he exploded, but later it was shown that he was still alive. In episode 46, Maribaron discovers that he was actually a host body for their boss. In episode 47, he was summoned when Black RX refused Crisis' order, killed as a resort as Crisis is revealed upon Dasmader's demise.
A small robot that announces Jark's arrival before his subordinates and transmits messages from Crisis himself. He was destroyed by Kamen Rider Black RX before the final battle with Dasmader.
The Crisis Empire's foot soldiers. They come in three colors: gray, brown and black. They later wear capes. The last of them were finished by the original 10 Kamen Riders before Black RX battles Dasmader.