Energy is the true leader of EXE and the main antagonist of the final episode of Kamen Rider W, as well as the final antagonist of the series overall.
Energy initially appears as a nameless worker at the pet shop where Shotaro went to buy cat food at the beginning of the episode.
After Shiro Endo and his EXE members were defeated by Shotaro and Terui, Energy showed and revealed himself as the true leader of EXE before transforming into the Energy Dopant to fight him.
The Energy Dopant shoots Shotaro with the railgun mounted on its arm, seemingly killing him. However, Philip shows up and blocks the shot before fusing with Shotaro to become Double Cyclone Joker once more. The two then defeat the Energy Dopant with their Joker Extreme Maximum Drive.