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!

The Yamazaki Ichimon, gathered as usual at Himuro’s (Yasukaze Motomiya) office, pushes to expand the Kenyukai office for more comfort. Ishizawa (Hiroto Honda) finally decides to buy a building, but Yamamura (Kenta Kawasaki), tasked with securing funds, hesitates. Just then, Ishizawa receives a call from one of his twin sisters, Arisa, showing an unexpectedly gentle side—until his expression suddenly hardens. Claiming it’s an emergency, Ishizawa reveals the truth: his other twin sister Marisa (Marina Mizushima) is simply crying after a fight with her boyfriend. Brushed off by his doted-on sister, Ishizawa asks Yamamura to check on her instead. Meeting Marisa in secret, Yamamura learns about her relationship with Tommy (Ken Mizorogi)—only for Ishizawa to erupt, insisting Tommy is a dangerous killer, sending the situation spiraling fast…

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.

Ryuji (Tatsuya Kishida), inspired by Kawakami’s (Tatsuya Nakazawa) coolness, comes to admire him deeply. Kawakami, however, feels uneasy around Ryuji, burdened by a past trauma inflicted by a certain man. Himuro (Yasukaze Motomiya), Tamura (Yoshiyuki Yamaguchi), and Saito (Katsuya), who know Kawakami well, sense something is wrong. Their fears prove true when Kawakami reunites with his old nemesis, Apollo (Tomohisa Yuge). Convinced that Kawakami is Yokohama’s strongest, Ryuji becomes obsessed with forcing a one-on-one fight between Kawakami and Apollo. Can Kawakami finally overcome his past trauma…?