The story is quite simple. Jun did “steal” Wakana from the mansion after the defeat of Terror to continues Gaia Impact Foundation X version. Knowing that plan, Shotaro receives last request from Phillip before vanished in next henshin. After Saeko revealed Jun’s secret lab, four of them (plus Terui and Akiko) storm it. Shotaro who doesn’t want henshin lets Accel to fight Utopia dopant (Jun) alone. Of course, Jun overwhelms Accel. Now the rest is up to Shotaro.
Phillip has prepared everything before last battle, from created a lie going to study aboard to everyone (Q&E, Santa-chan, etc) and LostDriver to let Shotaro protecting the city alone in Kamen Rider Joker form. After Utopia messing around, Shoatro decides to fight back by saving Wakana ALONE (thanks for all gadgets) and performing his last henshin with Phillip. W beats Utopia with Double Prism Xtreme rapid drop kicks, Twin Maximum of Prism memory on belt’s maximum slot and Xtreme memory. Oh yeah Saeko did help Phillip a lot as Taboo dopant. Kiriyama Renn did cry a lot too :)