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, witnesses 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 manages to stop the fight, and the Swallowtail Fangire reveals that the young woman was actually a renegade Fangire. Yusuke reveals he has promised to help Wataru because he is uncomfortable with being the King.

As Tsukasa is fighting against Kaixa in another dimension, the Beetle Fangire defeats Wataru and becomes the new Fangire king, claiming Kivat. After the new King dissolves the truce, Yusuke arrives to protect Wataru before the boy runs off. After Yusuke expresses his reasons for helping the dethroned boy, Wataru takes refuge in the Hikari Studio. After being caught up on current events, Tsukasa makes his way to Castle Doran to save Yusuke as the Beetle Fangire absorbs the Arms Monsters into himself. After destroying the Swallowtail Fangire, Decade encounters the Beetle Fangire, who assumes Kiva's DoGaBaKi Form. When their fight makes its way to Yusuke and Wataru, the boy finds his courage to overcome his Fangire impulses and declares himself the King once more.

When Natsumi realizes that this is the world from her nightmares, she becomes wary for Tsukasa's well-being. Finding him in a tuxedo and feeling that this is the final chapter to their journey, they witness Wataru and Kazuma leading their respective Rider/monster groups against each other. After Rising Ixa and Leangle are killed off in the fight, Tsukasa makes his way to Wataru as he grieves over Ixa's death. Meeting the Fangire Queen Yuki, they learn from Wataru that the Riders are fighting each other to maintain the existence of their worlds.

After fighting off the Riders, Super Apollo Geist takes Natsumi to be his new bride as he flees. Kazuma Kenzaki appears, saying that Tsukasa's existence is the real cause of the worlds blending before confronting him as Kamen Rider Blade in King Form in order to force him to leave the world at once with Asumu keeping Yusuke and Wataru from interfering as Decade is easily defeated.