Kamen Rider Arc is the Legendorga Lord and the main antagonist of the movie Kamen Rider Kiva: King of the Castle in the Demon World.
In the past, Kamen Rider Arc led the Legendorga race to war against the other Demon Races until he was defeated by the original Kiva and had his essence sealed within a coffin. Years later, the site of his imprisonment became the ground for a prison. Arc's coffin was later uncovered by a psychotic inmate named Takashi Sugimura as he was fleeing from the Zebra Fangire, allowing Arc to possess Sugimura's body. During the next 20 years Sugimura was in prison, he was sentencted to be executed several times but each time he did not die due to Arc.
After the Legendorga were revived in the present day, they brought Sugimura to Arc's castle where the demonic Rider resurfaced within him. Now fully revived, Arc led the Legendorga to conquer the world once more as well as gain control of the humans and any other race who opposed him. To ensure his conquest is unimpeded, Arc also sought to defeat the current Kamen Rider Kiva, Wataru Kurenai.
When Wataru and Otoya Kurenai faced off against Arc, Arc used Legendorga baptism to covert Wataru into a servant of the Legendorga, turning him into Kiva Flight Style. Arc then ordered him to kill his father, but Otoya manages to get through to his son and get him to resist his brainwashing. Wataru then fought against Arc and destroyed him as Kiva Emperor Form and Flight Style with assistance from Castle Doran.