Megaville Justiφ's (Kamen rider Faiz x Powerpuff Girls D)

Smart Brain corporation, the world's most powerful corporation, is trying to take over the world using Orphnoch, the "next stage in humanity's evolution", to covertly kill off the human population. In pursuit of this, they develop three suits of power armor, called Rider Gears (each for Faiz, Kaixa, and Delta), to find and protect the Orphnoch King, who can fix a defect within Orphnoch DNA which causes their genetic structure to break down, leading to death.

But the Rider Gears are stolen by Hanagata, the Goat Orphnoch and former chief of Smart Brain. He sends them to his foster children (dubbed the "Ryuseiji", after the school they attended) so they can stop the Orphnoch from achieving their goal. However, Rider Gears were designed to be worn by an Orphnoch, and humans are unable to activate the systems without undergoing genetic modification.

Eleven years after the events of Powerpuff Girls, The girls, Blossom, Bubbles, and Buttercup, now teens, move to Megaville, a bigger neighboring city of Townsville, along with their father, Professor Utonium. There, they are transferred to a new school called Megaville Academy and make friends with several other students like Dexter, a boy genius. But, at the same time, evil forces, both old and new, plan to take over the world with a new villain called Dr. X and his creation/daughter Bell. However, they're unknowingly dragged into conflict between Orphnochs and humans as Smart Brain corporation is one step ahead of heroes and villains in Megaville as they target Megaville as a big opportunity for their goal.

A young loner, Riku Inui, is unwittingly drawn into the conflict between the Orphnoch and humans and becomes Kamen Rider Faiz to save the life of students of Megaville High. Smart Brain begins targeting him in an attempt to retrieve the Faiz Gear.