Kiva's World
Wataru / Kamen Rider Kiva
Wataru is a 12 year-old half-Fangire boy from the Kiva World, having the ability to transform into Kamen Rider Kiva with the aid of Kivat-bat the 3rd. Referred to as the Prince by his servants, Wataru is reluctant to claim the title of King of the Fangires. He finds the overseeing of the ceasefire between humans and Fangires a very troublesome and unnerving task due to his fear of making friends and losing control over his Fangire impulses around them. But events leading to the Beetle Fangire attempting to disrupt the peace allows Wataru gets over this fear and takes his place as the official King of Fangires. He later appears in the World of the Rider War as his reality is absorbed into it. Leading the Riders of his world, Wataru refuses to listen to Tsukasa and Yusuke in uniting all Riders to defeat Dai-Shocker and stop the convergence of the worlds, while in grief over IXA's death. He even went so far to allow the Queen of the Fangires, Yuki, to marry Apollo Geist for the Kiva World to have an advantage over the other A.R. Worlds, but later changes his mind when the Fangire betrayed them to Dai-Shocker. After defeating Super Apollo Geist, the convergence of the worlds continues and the Kiva World and Wataru disappear. However, in Kamen Rider ? Kamen Rider Double & Decade: Movie War 2010, he is resurrected after Tsukasa has been killed by Kamen Rider Kivara. He later appears alongside the Riders of the Nine Worlds to revive Tsukasa and help him battle Super Shocker, assuming Emperor Form with the help of Decade's K-Touch.
Arms Monsters
The Arms Monsters are servants of Kiva, each the last of his kind. Composed of Garulu, Basshaa and Dogga, they support Kiva by turning into the weapons that allow Kiva to change form. They are absorbed into Beetle Fangire's breast plate and shoulder armor when they question their new king's intentions of removing the human/Fangire coexistence law. In addition to these alternate versions of the Arms Monsters, the original versions appear in the timeline within the World of Den-O in The Onigashima Warship, where the wayward Urataros, Kintaros, and Ryutaros hide within Jiro (Garulu), Riki (Dogga), and Ramon (Basshaa), respectively until they can be rescued.
Kivat-Bat III
Kivat-bat the 3rd is the third generation of the Kivat-bat Family. He formed a partnership with Wataru to give him the power of Kiva, attaching to the Kivat Belt to allow his human partner to transform and use other abilities through the Fuestles.
Kamen Rider Ixa
Masato Kusaka is a selfish young man who transformed into Kamen Rider Kaixa. In Decade, Kaixa is a wildcard Kamen Rider who attacks Decade after he is taken to another world by Kiva-la. He is under the impression that Decade is a hindrance to his own agenda and seeks to take the Decadriver from him. He eventually concedes when Decade is returned to the World of Kiva. Kamen Rider Kaixa reappears briefly in later airings of the series finale, using his Side Basshar to attack Decade and Wataru's group. He is seemingly killed in the chaos afterwards alongside many other Riders. In Kamen Rider Decade: The Last Story, Decade is shown to hold a Side Basshar card, labeled as a Kaixa card.
The Fangires
The Fangire Race are vampiric creatures that resemble stained glass, originally feeding off of the Life Energy of humans until they are commanded by their king to coexist with them. However, some of these Fangires are unable to follow this law due to their instincts. Each Fangire belongs to a specific class based on the animal form it takes. Several Fangires also appear in the first episode when Natsumi is trapped within the changing dimensions. They include the Shark, Moose, Horsefly, Rat, Mantis, and Seamoon Fangires. The Mantis Fangire later appears fighting the Beetle Fangire.

Ryo Itoya / Spider Fangire
In Episode 4, Ryo Itoya is a strange young man who is in actuality the Spider Fangire. He is the first Fangire that Tsukasa and Natsumi encounter, and reveals to them the truce that exists between Humans and Fangires while posing for a photo in the Hikari Studio.

Beetle Fangire
The Beetle Fangire/Attonement of the Garden Divided, the International Dateline, is the previous King of the Fangire Race and a member of Insect Class Tribe. He was exiled for loving a human woman who gave birth to Wataru. Seeing the coexistence and peace between the two races as nothing more than a farce for his son's sake, the Beetle Fangire breaks the peace by attacking humans to gather their Life Energy and reclaim his title, even stealing Kivat from Wataru. His actions of removing the law to restart past conflicts between the two races provide the motivation for Wataru to step up and truly claim his place as King of the Fangires. In the end, he is weakened by Decade's Kiva Arrow, then fatally wounded by a Dimension Kick/Darkness Moon Break combo. Revealing that he knew of the Fangire's true identity and intent before he dies, Tsukasa plays a final song for him before the man shatters.
Rook / Lion Fangire
In Episode 4, Fangire with the title of Rook, he is chasing after a renegade Fangire when Tsukasa interferes and destroys him with the Ride Booker's Decade Slash.
Bishop / Swallowtail Fangire
In Episodes 4-5, a Fangire with the title of Bishop, his task is to oversee the progress of all Fangires and their moral conduct, deeming those who are traitors to their king's laws. When the Beetle Fangire regains his title, the Swallowtail Fangire aides his master until he is shattered by Decade's Dimension Slash.
Series:  Kamen Rider Decade