In the windy city of Fuuto, detective Shotaro Hidari and his partner, the mysterious Philip combine to become the two-in-one Kamen Rider, W in order to fight creatures called "Dopants" that abuse the power of items called Gaia Memories.
A detective, Hidari Shotaro, and an unknown library-boy, Phillip, combine to become a half-green half-black hero to protect Fuuto City by using Gaia Memories.