In the city of Fuuto, criminals use USB-like devices known as Gaia Memories to transform into superpowered monsters called Dopants, causing chaos in the otherwise tranquil city. Yet, there are also heroes who employ Gaia Memories to combat these criminals, including the self-proclaimed, hard-boiled detective Shoutarou Hidari. Assisted by his witty partner, Philip, the duo transforms into Kamen Rider W—the legendary hero of Fuuto. Following the collapse of Museum, the evil organization behind many of Fuuto's crimes, the production and distribution of Gaia Memories have ceased. Nevertheless, remnants of Gaia Memories persist in society and are sold on the black market for high prices. Consequently, the two heroes from the Narumi Detective Agency have yet to find time to relax. Sightings of Dopants continue, and the agency receives an increasing number of clients reporting supernatural phenomena. Despite the arduous nature of their task, Kamen Rider W vows that those who harm Fuuto will inevitably pay for their sins.