Kamen Rider Kiva-la

Kamen Rider Kiva-la is a Kamen Rider appearing in Kamen Rider Decade: Final Chapter. Similar to other riders before her in the series, Kivala is an original Kamen Rider from an A.R. World. Though unlike them, Natsumi does not come from an A.R. World but uses powers from one.

Natsumi Hikari
Natsumi Hikari, referred to as Natsumikan by Tsukasa and Natsumelon by Daiki, is a young woman who works at the photo studio under her grandfather, Ejiro Hikari, having lived with him since childhood. Prior to the series, Natsumi was a member of the Taigaku Club or TG Club for short with friends that dropped out of high school to find their own answers in life. Unfortunately they never carried it out and went back to high school, promising to meet each again. At the start of the series Natsumi has nightmares about Kamen Rider Decade and later finds his belt and cards, giving them to Tsukasa. Knowing the dangers, Natsumi decides to accompany him on his journey.

She occasionally uses the Hikari Family Secret Laughing Pressure Point to keep Tsukasa and others in line. It's possible she has feeling or cares for Tsukasa's well being, hinted during her talk with Yuusuke. Despite Narutaki's offer to save her, Natsumi choose's to stay with Tsukasa until the end of their. However, she starts to worry after hearing from Narutaki that Tsukasa's actions are actually destroying the worlds rather than saving them. In the World of Shinkenger, she assure's that the Hikari Family Studio is Tsukasa's home. In the World of RX she is attacked by Apollo Geist's, Perfecter, draining her life until it was saved by Tsukasa giving up some of his own life energy. In the World of Amazon she starts to wonder if there is a point in there journey.

In the World of the Rider War, after being saved by Tsukasa, Daiki, Yuusuke, Wataru, and Asumu from Super Apollo Geist. Her nightmares become reality and the Rider War begins.

In Decade: Final Chapter Natsumi tries to convince the now Fury Form Decade to stop what he's doing but fails. She later becomes Kamen Rider Kiva-la to fight Decade and he lets her destroy him. Before disappearing Tsukasa gives her the Kamen Ride Cards he's received and the riders he defeated were revived.

After being told of Tsukasa's role, she seeks out a way to revive him and is successful by showing a picture of him to the A.R. Kamen Riders. Natsumi becomes Kivala again to stop Super Shocker with Tsukasa, Daiki, and Yuusuke and saves her grandfather after he reverts from Super Doctor Shinigami. She is last seen with her friends taking a picture after the conflict.

Megumi Aso
In the S.I.C Hero Saga side story King of Vampire (which is an alternate ending to Kamen Rider Kiva), at the end of the wedding Kiva-la shows up instead of Masao Kurenai to warn everyone about the threat of the Lion Fangire's Sabbat. Kiva-la chooses Megumi to become Kamen Rider Kiva-la.

Kamen Rider Kiva-la
Natsumi uses a similar transformation method to Kamen Rider Kiva to transform into Kamen Rider Kivala. Unlike Kiva she lack Fuestles but makes up for this with the Kiva-la Sabre which she uses to perform her finishing attack, Sonic Stab.

Kiva-la Belt
The Kivala Belt is a transformation belt similar to the Kivat belt used by Kiva. Unlike Kiva the belt does not materialize first and does not require Kivala biting the body but kissing the forehead creating a heart emblem.

Kiva-la Saber
A weapon used by Kivala which she uses to great effects. Unlike Kiva she does not require Fuestles to perform her finishing attack, Sonic Stab. Doing so allows enables her to sprout energy wings while attacking similar to Kiva Emperor Form's Emperor Moon Break.

Trivia:

 * Originally Kamen Rider Kivala was going to be the true form of Kivala, as shown in the original trailer for Kamen Rider X Kamen Rider W & Decade: Movie War 2010 attached to the finale.