The Fumen Master is a minor but recurring character who originates from the television series Kamen Rider W and makes a cameo appearance in the film OOO, Den-O, All Riders: Let's Go Kamen Riders. His background is that of the friendly owner and operator of a small ramen cart called Fumen, which he runs in Futo City, the primary setting of Kamen Rider W. His real name is never revealed, and he is known simply by his title as the Master.

In terms of personality, the Fumen Master is depicted as an easygoing and positive individual who takes genuine pleasure in serving his signature ramen dishes to anyone who stops by his cart. His forgiving nature is a key trait; even when wronged by others, such as Izo Aida, who attacked him while transformed into the Oyakodon Dopant, the Master chose to pity him rather than hold a grudge, eventually offering him a job. This optimistic outlook, however, can sometimes make him unaware of negative events happening around him, such as petty crime. In his appearance within Let's Go Kamen Riders, his core motivation is simply to seek help, as he is shown begging for assistance from the detective duo Shotaro Hidari and Philip, who transform into Kamen Rider Double to fight against the forces of Shocker.

The Fumen Master's role in the story of Let's Go Kamen Riders is that of a minor ally and a civilian in need of rescue. He does not drive the main plot involving the time-traveling Kamen Riders OOO and New Den-O, but his scene helps to establish the presence of the Shocker organization and the ongoing threat they pose, while also providing a brief moment for Kamen Rider Double to appear and assist. His key relationships are with the protagonists from Kamen Rider W, Shotaro and Philip, whom he knows from his regular appearances in their city. He is also shown to have a relationship with his employee, Izo Aida.

The character does not undergo any significant development within this particular film, serving more as a familiar face for audiences of Kamen Rider W. His notable abilities are not combat-oriented; instead, he is a skilled ramen chef who has created unique dishes for his cart, such as ramen topped with a large narutomaki fish cake. With Izo's help, he also devised a new Futo City delicacy called Futodon. While his business is small, it is portrayed as being quite successful due to the quality of his food and his amiable nature.