Criminals in Fuuto use USB-like devices called "Gaia Memories" to transform themselves into superpowered monsters known as "Dopants," wreaking havoc on the otherwise peaceful city. However, there are heroes who use the Gaia Memories to fight these criminals, one of whom is Shoutarou Hidari, the self-proclaimed hard-boiled detective. The two transform into Kamen Rider W—the legendary hero of Fuuto City—with the help of his witty partner Philip. The production and distribution of Gaia Memories has ceased since the fall of Museum, the evil organization responsible for many crimes in Fuuto. However, remnants of Gaia Memories still exist in society and are sold at high prices on the black market. As a result, the two heroes from Narumi Detective Agency have yet to appear.