The story begins with a regular day with Takumi, Mari and Keitaro, which suddenly turns into a musical number thanks to a mysterious new boom box created by Smart Brain. As it turns out, Yuji, Yuka and Naoya have the same boom box and are greeted by a rapping Smart Lady who reveals that it's part of a new plan by Smart Brain to invoke people into singing all over Japan. The reason: To get the three Rider Belts back!
Ishizawa (Hiroto Honda) finally decides to purchase a building for his group, but Yamamura (Kenta Kawasaki), who is entrusted with financing by Ishizawa, is full reticence in how to go about doing so. Just then, Ishizawa receives a phone call from one of his little sisters, Arisa, and a plot unfolds involving marriage scams, murder, and the tunnel-vision of an overprotective elder brother...
The Hyodo-gumi boss—part of Tendokai, Japan’s largest yakuza syndicate—has been brutally murdered. Kazuma Washio (Hitoshi Ozawa), the head of the Washio-gumi and Tendokai’s wakagashira (underboss), is convinced that Yoshinari Myojin (Sho Aikawa), a former Tendokai wakagashira-hosa now running Tokyo’s underworld of thugs and mafia, is behind the killing. Around the same time, Tendokai's 5th-generation chairman Katsushige (Hakuryu) orders Washio to secure a woman named Nagi Toyama (Akane Hotta). Washio sets out with his men, Okita (Yasukaze Motomiya) and Date (Hideo Nakano), but they’re ambushed by a group of heavily armed youths. Barely escaping, they manage to bring Nagi to their hideout—only to discover she’s a key player in a power struggle over the Tokyo Casino Project. And so begins the greatest conflict yet, entangling yakuza, mafia, street gangs, the police, and even the state itself—
In the near future, the world is ruled by the Smart Brain Corporation, with 90% of the population being Orphnoch, and the once prominent human race is nearing extinction. Takumi Inui, Kamen Rider Faiz, was once regarded as mankind’s savior until, in an attack by Smart Brain troops, he was presumed dead. Since then, human rebel groups have staged attacks on Smart Brain’s complex in an attempt to steal the top-secret Emperor Belts, with no success. Kiba Yuji, Naoya Kaidō and Yuka Osada attempt to ease tensions between both races but their peace meeting is interrupted by Smart Brain troops and their newest warrior, Kamen Rider Psyga. Takumi, believing himself a young cobbler named Takeshi, regains his memory and becomes Kamen Rider Faiz again to settle things with Smart Brain once and for all.