Kamen Rider Aqua

Aqua unlike Poseidon, does not use Core Medals but water as energy to transform. Aqua appears to based on the Double Riders, Kamen Rider #1 and #2, but is powered by water instead of wind. His Rider Kick is called the Oceanic Break.

Aqua Miraider

Unlike the Kamen Riders of the past, instead of a motorcycle, Aqua's Rider Machine is a jet ski called the Aqua Miraider. Miraider is a portmanteau of Mirai (which means Future) and Rider.