Akiko Narumi
Akiko Narumi is Shotaro's boss and landlord at the Narumi Detective Agency. Because of her young appearance and attitude, Shotaro refers to her as "Middleschool Girl" and sees her as a threat to his public image. She has come to Futo from Osaka to continue in her father's place, initially unaware that her father died until the events of the Begins Night film. She serves as a personal assistant while on the job as well as keeping Shotaro on the right track by slapping him with a green sandal; she has also used this tactic on other characters, including Dopants. She has a black and white view of the world and tends to say "I won't hear of it!" (when she is caught off guard by something). Despite her somewhat childish personality, she has shown signs of promise as a detective, particularly in her ability to decipher clues that leave Shotaro, Philip, and Ryu stumped, as well as being extremely protective of clients, a trait she shares with her father. Akiko harbors a crush on Ryu Terui, but her advances are ignored as he maintains a professional demeanor towards her, until he finally gives in to his feelings for her. She marries Ryu in Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie War Core.
Mikio Jinno
Mikio Jinno is a senior detective of the Futo Police working on the Dopant case who is very gullible, falling for the same trick every time until the Jewel Dopant case when he is arrested and vows to himself to be less gullible after being cleared of all charges. He also happens to be a friend of Shotaro's with whom he discusses cases, while unaware of his Shotaro's connection to Kamen Rider Double. He is almost never seen without his back scratcher.
Shun Makura
Shun Makura is Jinno's rookie partner, a pleasant guy who is naïve of Shotaro's skills. He and Shotaro often get into fights when they are together, at times requiring Jinno to break them up. He is extremely impulsive, often jumping to conclusions when it comes to solving crimes and accusing people of committing crimes with little or no proof.
Watcherman (is the username of an otaku blogger who is Shotaro's informant on Dopant activities. He also owns a bicycle called Futo-kun Bicycle that he won in a mail-in contest.[4] During the events of W Forever, Watcherman obtains the T2 Violence Memory and it forces him to become the T2 Violence Dopant, whose left arm and Violence Ball form are pure destruction. After being restored by Double LunaJoker's Joker Strange Maximum Drive, Watcherman is taken to a free clinic where he stays during NEVER's attack.
Santa-chan is a mysterious man who is seen throughout Futo, the owner of a pet shop who promoting local companies in a Santa Claus outfit. He gives out presents which always seem to help out the recipient. During the events of W Forever, Santa-chan obtains the T2 IceAge Memory and it forces him to become the T2 IceAge Dopant, with the ability to make absolute zero ice. After being restored by Double LunaJoker's Joker Strange Maximum Drive, Santa-chan is taken to a free clinic where he stays during NEVER's attack. One year after the final battle with the Utopia Dopant, Santa-chan is seen as the owner of a pet shop that Shotaro visits, breaking up a fight between Shotaro and an unnamed employee who is later revealed to be the Energy Dopant.

Queen & Elizabeth
Queen and Elizabeth are two teenage girls who serve as Shotaro's informants in high school settings. The two are also singers, who get a major label release for their song "Love?Wars". In Begins Night, it is revealed that Elizabeth has feelings for Philip. During the events of Kamen Rider W Forever: A to Z/The Gaia Memories of Fate, Queen is seen with the T2 Queen Memory, which can be used to form a barrier around the user. The Gaia Memory attempts to take control of Queen and forms a Living Connector on her arm, but she is able to resist and throw the Memory away. Elizabeth also finds the T2 Accel, Key, and Bird Memories, giving them to Shotaro without being affected by them.
"Master" is the owner of "Fumen" ramen cart where citizens of Futo like to eat. His sepcialty is making ramen with large sized narutomaki. During the events of Hyper Battle DVD, he is attacked by the Oyakodon Dopant. However after it is revealed to be Izo Aida, Master of the OmuriFu restaurant, he takes pity on him and hires him to work with him at his ramen cart. As a result with Izo's help, Master devises a new Futo delicacy: "Futodon".

In the webisode "The U is a Mystery!/Rondo" of the Net Movies, he becomes the UFO Dopant while Jinno and Makura were experimenting the UFO Memory. He later travels into outer space as the UFO Dopant.

Series:  Kamen Rider W