Akiko Narumi arrives in Futo to be the landlord of the "hard-boiled" detective Shotaro Hidari, who finds himself involved in a case involving an old friend and a Dopant.
After his missing target is killed by another Dopant, Shotaro works with his partner Philip to figure out the truth regarding the killer while being dogged by Akiko and her strange sightings.
Shotaro tries to find the Cockroach Dopant's identity - in order to regain Double's missing Gaia Memories. Meanwhile, Philip tries to reunite the dance partners for their legendary move.
When the search for the Virus Dopant takes an unexpected turn, Shotaro and Philip must work to find the true controller and the reason behind their grudge.
Discovering a horrible secret from Saeko and seeing his partners captured by Arms Dopant, Philip must figure a way to save them even if using the unstable Fang Memory.
As Ryu's intensity threatens to harm innocents, Shotaro and Philip must discover the reason behind his anger while putting a stop to the ice-powered Dopant.
As Horinouchi is taken by the bizarre Shinkuro for further usage, Akiko tries to decipher the meaning of the doll and the truth behind Horinouchi's daughter.
An air-headed female magician who turns invisible asks Shotaro to find the seller of her Gaia Memory, which ultimately leads Ryu to the man who killed his family.
As Philip is taken by the Xtreme Memory to meet with Shroud, Shotaro continues to try and figure a way to discover the culprit behind Nightmare Dopant's attacks.
After being in prison for 10 years, an old client of Sokichi's asks Shotaro to help him uncover some information - which he had asked Sokichi to look into before being arrested.
As Shotaro is asked to pursue a young teacher by her students, Ryu also goes after her due to a remarkable similarity between her and his deceased sister.
As Akiko desperately tries to complete Toru's movie, the insular director is targeted by Wakana for allowing her to access the full potential of her Dopant power.
Shotaro and Ryu are asked by a mother to save her daughter, who has become an old woman. Meanwhile, Shroud wants Phillip and Ryu to become Kamen Rider Double CycloneAccel Xtreme.
Ryu tries to decipher the truth regarding Shroud and her true purpose as she tries to force him and Philip to join together into the ultimate W to defeat Ryubee.
With Shotaro trapped in fear and Ryu injured, Philip is at the mercy of his father Ryubee, who prepares to use his deceased son and Wakana to bring about Gaia Impact.
Shotaro and Philip must endure the ultimate hardships in order to stop Kazu from completing his own Gaia Impact to complete what could be their final case together.
One year after Philip's departure, Shotaro continues onward; but a case involving saving a boy's sister from Dopant thugs brings forth a change for the better.
