Kamen Rider W is set in the fictional city of Futo, where a mysterious figure known as the Dopant has begun to wreak havoc. The story follows two main characters, Shotaro Hidari and Philip, who become the hosts for the Kamen Rider W. Using their unique abilities and the powers of the Gaia Memories, they transform into Kamen Rider W, fighting against various enemies and unraveling the mysteries behind the Dopant.