|This article is about a/an alternate reality/A.R. World (another rider's world) in Kamen Rider Decade.|
The World of Kiva (キバの世界 Kiba no Sekai) is the alternate reality where a version of Kamen Rider Kiva takes place. Unlike the original series, this world allows Fangires and humans to coexist, with the King's servants destroying the rebellious Fangires. The backdrop that allows entry into the World of Kiva depicts a nighttime cityscape with Castle Doran emerging from a building. Within this A.R. World, Tsukasa assumes the identity of a violinist with the talent of playing violin solo similar to those of Otoya and Wataru Kurenai.
Arriving in the World of Kiva, Tsukasa and company discover that the Fangires of this world have made a truce with the humans. However, when Tsukasa finds the Lion Fangire attacking a young woman, he transforms into Decade to fight him. Wataru, the King of the Fangire Race, witnessed this and becomes Kamen Rider Kiva to fight him with the aid of his Arms Monsters, forcing Decade to assume Kamen Rider Kuuga's Mighty, Titan, and Dragon Forms to counter. Yusuke managed to stop the fight, and the Swallowtail Fangire revealed that the young woman was actually a renegade Fangire. Yusuke revealed he had promised to help Wataru because he was uncomfortable with being the King. After meeting a mysterious man who was disgusted with the human/Fangire treaty, Tsukasa later encountered Kiva-la, who used her power to send him into another world where he is attacked by Kamen Rider Kaixa. Back in the World of Kiva, after having fed on many humans, the Beetle Fangire arrived at Castle Doran with the intent to kill Wataru and take his place as the King.
As Tsukasa was fighting against Kaixa in another dimension, the Beetle Fangire defeated Wataru and becomes the new Fangire king, claiming Kivat. After the new King dissolved the truce, Yusuke arrived to protect Wataru before the boy ran off. After Yusuke expressed his reasons for helping the dethroned boy, Wataru took refuge in the Hikari Studio. After being caught up on current events, Tsukasa made his way to Castle Doran to save Yusuke as the Beetle Fangire absorbed the Arms Monsters into himself. After destroying the Swallowtail Fangire, Decade encountered the Beetle Fangire, who assumed Kiva's DoGaBaKi Form. When their fight made its way to Yusuke and Wataru, the boy found his courage to overcome his Fangire impulses and declared himself the King once more. He took back the Kiva power and helped Decade battle the Beetle Fangire, mortally wounding him with a Darkness Moon Break/Dimension Kick combo. Later, Tsukasa paid a final visit to the Kurenai manor to play a final song for the dying Beetle Fangire, whom he knew was the man he met earlier and was Wataru's father.
Wataru later appears in the World of the Rider War as his reality is absorbed into it. Leading the Riders of his world, IXA and Saga, 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 World of Kiva 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 World of Kiva and Wataru disappear. However, in Kamen Rider × Kamen Rider W & Decade: Movie War 2010, he is resurrected after Tsukasa has been killed by Kamen Rider Kiva-la. 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 and later uses Castle Doran to fight the Super Crisis Fortress.
After Ultimate D was defeated with the combined power of Decade and Kamen Rider W, Wataru went back to his world and it can be assumed that he is still King and is maintaining the Fangire/Human Coexistence.
- Wataru (Kamen Rider Kiva)
- Kivat-bat the 3rd
- Kamen Rider Ixa
- Kamen Rider Saga
- Arms Monsters
- Ryo Itoya (Spider Fangire)
- Beetle Fangire
- Yuki (Thorn Fangire)
In the novel reimagination of the Kamen Rider Decade TV series, Kamen Rider Decade: The World of Tsukasa Kadoya ~The Garden Inside the Lens~, the World of Kiva is, as one of the Nine Worlds, not an alternate reality like in the TV series but the original world. The World of Kiva is one of the six worlds the Hikari Studio group, Tsukasa/Decade, Kaito/Diend, and Natsumi, have already traveled to by the start of the novel as they head for the three remaining worlds, and thus not much is seen about it.
- Oddly enough, this world sees Fangires and Humans coexist. In the Kamen Rider Kiva TV series proper, it's the opposite; Fangires pose a threat to the human society, and the Queen imposes the law to Fangires to punish those who build a relationship towards a human.