|“||Don't think this is it! Your fates are already set... by that woman named Shroud! I will be waiting for you in Hell!||„|
|~ Isaka's final words|
Shinkuro Isaka, who uses the Weather Gaia Memory to become the Weather Dopant, is a member of the Museum and a major antagonist in Kamen Rider W. He is the main antagonist of W's second arc as the arch-enemy of Kamen Rider Accel.
He was portrayed by the late Tomoyuki Dan.
Dr. Shinkuro Isaka was the 42 year old head physician at the Isaka Medical Clinic. Ten years before the start of the series, Isaka wandered on the street while finding no meaning in his life. For an instance, he encountered Ryubee Sonozaki attacking a group of people after transforming into the Terror Dopant. Overjoyed and mesmerized by witnessing Terror Dopant's power, Isaka swore his loyalty to Ryubee and begged the latter to give him Terror Memory. Ryubee only responded that Isaka should earn one by himself before he left.
Obssessed with earning the Terror Memory, Isaka experimented on himself with numerous Gaia Memories with various Living Connectors on his body before Shroud gave him the Weather Memory in the hope that he would be powerful enough to eliminate Ryubee. However, much to Shroud's horror and regret, Isaka went more and more psychotic after gaining the power of his new Gaia Memory. He originally tested these abilities in a series of freezing, electrocution and drowning murders. He killed many people, including Ryu Terui's family, to whom he was only known as the "man with the W Memory". Later, he officially joined Museum as a top executive in order to gain Terror Memory for himself.
During his failed attempt to add the Invisible Memory to his arsenal, Isaka was exposed and took refuge in the Sonozaki Family estate. There, he convinced Saeko Sonozaki to take out her father so she can control the Museum and he can get the Terror Memory. Though he originally sees Saeko as merely one of his pawns and research material, he admits to having developed feelings for her.
During his attempt to absorb the Quetzalcoatlus Memory, the Weather Dopant was finally defeated by Kamen Rider Accel Trial's Machine Gun Spike Maximum Drive, shattering the Weather Memory. Shortly afterwards, Isaka's body was covered in Living Connectors due to his excessive use of Gaia Memories. With his dying breath, he cursed Kamen Riders and revealed that Shroud would be their end, seconds before he crumbled into dust.
- Ryoko Gi, the actress who portrayed Suzuko Arima/Bell Dopant in Kamen Rider W and Yoshiko Tajimi in Kamen Rider Build, is the widow of the late Tomoyuki Dan, the actor who portrayed the role of Isaka.
- Tomoyuki Dan passed away on October 10, 2013, at age 50, only a few months after reprising his role as Isaka/Weather Dopant in the video game Kamen Rider: Battride War. As a result, this is one of his final roles.