Natsumi Kiva-la is a character from the Kamen Rider Decade and Kamen Rider Kiva universes, appearing in the crossover movie 'Kamen Rider × Kamen Rider W & Decade: Movie War 2010.' Natsumi Hikari transforms into Kamen Rider Kiva-la using the Kiva-la belt, taking on the power of the Kiva-la Fangire. As Kiva-la, she plays a key supporting role, assisting the main Riders in their battles and bridging the gap between the worlds. Her transformation marks a pivotal moment in the movie's storyline.