|This article is about a/an transformation device/ally in Kamen Rider Decade.|
She is extremely tiny, small enough to be hidden in an adult's closed fist. She learns of Tsukasa Kadoya from Narutaki and uses her power to bring Yusuke Onodera into her world, and then sends Tsukasa into another to do battle with Kaixa. She later ends up traveling with the Hikari Studio, though remaining in contact with Narutaki with only Natsumi aware of it. She seems to like Yusuke the most out of the traveling group as she is delighted when he returns to travel with them after they leave the World of Agito.
In Kamen Rider × Kamen Rider W & Decade: Movie War 2010, Kiva-la is revealed to be the means for Natsumi to assume her Kamen Rider form: Kamen Rider Kiva-la. It can be assumed that she is now a full ally to the group after these events.
In Kamen Rider Decade: Final Stage, she shows the ability to reverse time, twice, in order to help Tsukasa preventing the rampage of Diend.
Kamen Rider Battride War
Kiva-la appears as a navigator in the video game Kamen Rider Battride War.