A former fighter whose sharp instincts, well-trained pectorals, and sheer guts are second to none. He is a hot-blooded man with a straightforward heart. Permanently banned for a fixed match and arrested on suspicion of murdering Takumi Katsuragi, a former researcher at the institute, he escaped from prison. After successfully evading pursuers with Build's help, he shares his fate with Sento. Though he initially acted only to clear his own name, he is inspired by Sento's conviction for justice and eventually decides to fight alongside Kamen Rider Build as Kamen Rider Cross-Z.

Soichi Isurugi's daughter. A girl who is foul-mouthed but kind at heart. Possessing the special ability to purify components extracted from Smash, she was captured by Faust and forced to purify Smash Bottles, but she escaped the organization and hid in the secret base beneath the café "nascita." In addition to refining Fullbottles, she supports Sento Kiryu's activities by collecting information on Smash appearances as the popular net idol "Mi-tan." After purifying a bottle, Misora says, "I'm tired, I'm sleepy, and I want my wages," and heads straight to bed to sleep. She can only purify one bottle at a time.

He uses greetings like "Ciao." An astronaut who conducted manned Mars exploration. He is Misora's father and the man who discovered the Pandora Box during the "Kiwami Project" manned Mars exploration ten years ago. The coffee the Master brews tastes terrible, and no customers ever come to nascita.

A 27-year-old freelance journalist. She speaks with a gentle tone.

35 years old. The Touto Government Prime Minister's Aide and the Director of the Touto Institute of Advanced Matter Physics (a high-ranking member of Faust). Ten years ago, he attended the Mars probe return ceremony on behalf of his father, Taizan Himuro. After being exposed to the light of the Pandora Box, he developed a bellicose personality and began operating behind the scenes as the Faust executive Night Rogue, hidden by his title as the Prime Minister's Aide.

Age: 28. He works as Gentoku Himuro's secretary in Touto. He monitors Sento, who has been assigned to analyze the Pandora Box.

A young man who runs a farm called "Sawatari Farm" in Hokuto. He was a large landowner with 100 hectares of land, but the soil changes caused by the Skywall Disaster devastated the farm. To provide for his employees' living expenses, he volunteered for Faust's human experiments. As Hokuto's Kamen Rider Grease, he was initially in conflict with Sento Kiryu (Kamen Rider Build), but after Hokuto was occupied by Seito, he joined Sento and the others to end the war as quickly as possible. He is called "Kashira" (Boss) by his comrades Akaba, Aoba, and Kiba and is beloved by his employees. He also has a side as a huge fan of "Mi-tan."