Decade's World
Sayo Kadoya
Sayo Kadoya is Tsukasa's younger sister. She is a pianist and is protected by Nobuhiko Tsukikage due to her possession of the Stone of the Earth, which is the source of Dai-Shocker's travel between the A.R. Worlds. This allows her to become High Priestess Bishium, whom Shadow Moon manipulated to hate Tsukasa and turn Yuusuke into her puppet. After realizing that she has been used, she destroys the Stone of the Earth and later makes amends with Tsukasa before he leaves
Joji Yuki
Joji Yuki is a mysterious young man with a prosthetic arm who has the ability to become Riderman. He was a scientist who worked for Dai-Shocker and was involved in the production of the Decadriver and the Diendriver. For unknown reasons, Yuki rebelled against Dai-Shocker and was punished through the amputation of his arm. This has made him a wanted man in the Decade World.
Shouichi Tsugami
Shouichi Tsugami is the original Agito and he is played by the original actor. Shouichi briefly appears in the end of the movie along with Kotaro.
The mysterious Dai-Shocker organization is a conglomation of all villain organizations who set into motion a plan to take over all dimensions due to someone providing the means to do so. Their insigna is double-headed version of Shocker's eagle crest, but with the "DCD" written on it that hints at Decade's ties to them. In addition to Doctor Shinigami and Apollo Geist, there are many other members of Dai-Shocker that come from previous Kamen Rider Series. They sent their agents out across the worlds for universal domination.
Nobuhiko Tsukikage / Shadow Moon
Nobuhiko Tsukikage is a butler who takes care of Sayo and convinces her to become Bishium as part of his plan take over Dai-Shocker in the Decade World. Through the Stone of the Moon, Nobuhiko can transform into Shadow Moon. Once he ousts the former leader of Dai-Shocker, Tsukasa Kadoya, Nobuhiko becomes its leader as he leads the group to hunt down every Kamen Rider. In the end, though he overpowers Decade and Kuuga, Shadow Moon is defeated by Double and destroyed by the All Rider Kick.
Ambassador Hell
Ambassador Hell (is an executive member from the terrorist organization Shocker, originally from the World of Kamen Rider and donning a new black armor. He is able to assume the form of the Inhumanoid Garagaranda, a rattlesnake monster. In the final battle, he fights Kamen Rider 1, 2, Kabuto, and Black RX. He is killed when Riders 1 and 2 use a Rider Double Kick on him after being stabbed by Kabuto and impaled by Black RX, he praises Dai-Shocker before finally succumbing to his wounds and dying in a huge explosion.
General Jark
General Jark is a supreme commander from the Crisis Empire from the World of Black RX. He is killed by Diend.
King Dark
King Dark is a giant robot and the mastermind behind the Government Of Darkness (GOD) from the World of X-Rider. He is killed by Decade Complete Form Jumbo Formation.
Dai-Shocker Soldiers
The Dai-Shocker Soldiers (are footsoldiers of Dai-Shocker, resembling the Shocker Soldiers and tending to scream out "Yeee". They are able to assume missile-like forms.
Series:  Kamen Rider Decade