|This article is about a/an planet in Kamen Rider: Dragon Knight.|
The people of Karsh look like standard gray aliens and are able to assume a human form, presumably mostly for disguise; Xaviax also has a black monster form, though this is simply battle armor, as he is an army general. Although Xaviax was also able to disguise himself as Kit, Frank, and Eubulon (even mimicking his Advent Deck), it's unknown if the other inhabitants of the planet can also take on other forms. Eubulon is shown capable of generating a ball of energy that can place someone in a healing trance, and both he and Xaviax can control mirrors leading to and from Ventara by waving their hands, though either of these may be the result of an advanced technology instead of a natural ability.
Xaviax was the general in the planet's North Army while Eubulon developed weapons for him in their war against the south. The North won, but Karsh was turned into a wasteland.
Xaviax wanted Eubulon to find slaves from other worlds to rebuild their planet, starting with Ventara. Upon arrival, Eubulon fell ill and almost died, until a Ventaran Family took him in and helped him recover. Eubulon then realized that he couldn't destroy a world of good people and told Xaviax that they would have to find another way to save Karsh. Xaviax, however, wouldn't listen and decided to do it himself, sending an army of Mirror Monsters to attack.
Eubulon told Ventara's leaders what was coming and created the Advent Decks and Cards, while the Ventarans recruited twelve people to transform into the Kamen Riders to fight the Mirror Monsters and protect Ventara. Their efforts kept the Monsters at bay until Xaviax and Eubulon fought, with their attacks seemingly defeating each other. The Kamen Riders then went into stasis sleep, with each of them taking one-year awake shifts to keep Xaviax's remaining straggler soldiers at bay.
Many years later, Xaviax returned under the guise of "Parrigon", claiming to be a Karshan refugee and tricked Adam, the original Dragon Knight, into letting him into the Riders' stasis room, venting most of the Ventaran Riders. Emergency systems woke Len and Kase and they escaped, but Xaviax planted teleportation beacons and transmitters across Ventara, teleporting the planet's population except for Adam and his girlfriend Sara to Karsh to become slave labor; Adam and Sara then lived in a simulated world, unknown to Sara, as Adam's reward for his "help".
Xaviax then turned his attention to Earth, sending more Monsters to kidnap people to get a wide sample of DNA profiles and programmed the teleporters to kidnap them too. After Len/Wing Knight began hampering his efforts, he gave the other Advent Decks he stole to the Ventaran Riders' Earth counterparts, tricking each of them into wanting to defeat him for different reasons. In particular, he played a long game with Kit Taylor, the new Dragon Knight, letting him ally himself with Len before trying to use saving Kit's previously missing father, Frank Taylor, from a vegetative state to convince him to switch sides. It didn't work, and after losing his other Riders, he vented Kit. However, as Xaviax began placing his beacons and transmitters, Eubulon returned as well as three of the Ventaran Riders and provided them and the No-Men with a virus to disable the latter.
Xaviax then turned back to Adam, returning the Dragon Knight deck and sending him to infiltrate his old freinds and bring back a sample of the virus. After the return of Kit and Kase, and endless suspicion and resistance, Adam is finally trusted with the virus to disable the transmitter in North America, which he quickly hands over to Xaviax, who manually shuts the transmitter down to make it look like the virus worked. While decoding the virus to create a vaccine that would reactivate his transmitters, Xaviax sees Adam having second thoughts and disguises himself as Eubulon to attack and berate Adam to get him to stay on his side, this time out of free will.
However, when confronted by Len, Kit, and Kase, and feeling truly sorry for what he did, Adam revealed that he gave Xaviax the virus and that he had developed a vaccine. With the transmitters reactivated and slowly gaining power, Adam soon joins the other Ventaran Riders, Kit, Maya Young, Trent Moseley, and Eubulon in their final assault against Xaviax. Once the transmitters were at 100% power, Xaviax prepared to teleport the entire population of Earth to Karsh, but Eubulon interrupts him. Xaviax berates Eubulon for abandoning his own people, but Eubulon justifies his actions by pointing out that Xaviax destroyed Karsh, and that he couldn't let him destroy another planet. Xaviax refused to let their race die out, declaring Karsh and it's people superior, even though Eubulon says that their time of existence is done.
After the 13 Riders gather and combine their Link Vent cards, defeating Xaviax for good, they were able to move all of the beacons and transmitters from Earth to Karsh and bring the people of Ventara back to their home world, while Karsh either remained a ruined wasteland or was completely destroyed.