|This article is about a/an villain in Kamen Rider W.|
- ―Transformation announcement[src]
The Virus Dopant (バイラス・ドーパント Bairasu Dōpanto) normally turns its user into the vector of a deadly plague that can wipe out entire cities. However, when Sachi Yamamura (山村 幸) uses the Virus Memory to save herself from a hit and run, the transformation into the Virus Dopant is interrupted leaving only her consciousness fully enveloped in the Gaia Memory's corruptive influence. These events weaken the Virus Dopant, but also enables it to infect inanimate objects and electronics to compensate.
This ability leads to the creation of the "Infected Car", a formerly wrecked SUV that infects a human with its deadly virus upon impact. When the car is wrecked by Kamen Rider Double, the Virus Dopant begins using its physical form to exact Sachi's revenge on her ex-fiance who she learned was only a con man.
After discovering the Virus Dopant's vulnerability to heat, Double unleashes HeatTrigger's Trigger Explosion Maximum Drive to destroy the Dopant's physical body, causing the Virus Memory to eject from Sachi's body and shatters.