Kamen Rider Build: Be The One is the summer movie tie-in of Kamen Rider Build, released on August 4, 2018.
Following the Japanese Civil War in Builds timeline, Seito, Hokuto and Touto are now all led by governors instead of prime ministers and actively working to reunify Japan. However, the governors are secretly part of an evil alien race called the Blood Tribe who seek to destroy Earth and consume it. Deeming Sento Kiryu/Kamen Rider Build a threat to their goals, the three initiate their Build Destruction Plan, brainwashing the population of Japan and Sentos friends against him.
Kamen Rider Build: Be The One features examples of:
- 11th-Hour Superpower: Late in the movie, Sento tells Ryuga that if a Fullbottle that resonated with someone of Hazard Level 7 is used with another similarly evolved Fullbottle, they can overcome the limits of the organic/inorganic combination and become a Best Match. Vernage then emerges from the sidelines with Sawas help, and proceeds to give a portion of her power to combine the Genius Fullbottle with the Gold Rabbit and Silver Dragon Fullbottles, creating the Cross-ZBuild Can.
- Ain't Too Proud to Beg: Gentoku winds up having to beg to Utsumi again to let him and Kazumi out after theyve been captured.
- Anti-Mutiny: The other Blood Tribe members were initially subservient to Evolt, but when he decided to toy with the humans instead of instantly destroying the Earth once he obtained Black Hole like they intended, they defect from him to carry out the original plan.
- Big Bad: Evolt decides to sit this one out. Instead its his three Blood Tribe cohorts who are out to destroy the world and the ones who brainwash the citizens of Japan into turning against Sento.
- Cerebus Retcon: All of the events of the series so far have been revealed to have occured as a result of the machinations of the villains for this movie, Evolt's three former cohorts.
- Corrupt Politician: The three governors, members of the Blood Tribe who brainwash everyone in Japan into turning against Sento.
- Early-Bird Cameo: The Post Credits Scene features the introduction of Kamen Rider Zi-O.
- Evil Versus Oblivion: A rather weird case. The three villains are opposed by Evolt himself, since they want to destroy Earth in an instant, while Evolt wants Earth alive just so he can continue his sick "game".
- FaceHeel Turn: Ryuga is brainwashed into turning against Sento.
- Fugitive Arc: The new leaders of the three regions manage to unify Japan again, by turning them all against Sento/Build. Although there is some mass brainwashing involved.
- Fusion Dance:
- Kamen Rider Blood is the power booster variety, with Kengo absorbing his two Dragons, transformed into their Lost Smash forms, and Ryuga through the Snap Ride Builder to transform.
- In the Final Battle, Sento and Ryuga transform together into Kamen Rider Cross-ZBuild to take on Kamen Rider Blood.
- Free-Fall Fight: The Final Battle between Blood and Cross-ZBuild is on Bloods Doomsday Device descending to the Earths core. Funnily enough, the Finishing Move carries Blood all the way back to the surface to kill him.
- The Man Behind the Man: The Blood Tribe are shown to have been the true instigators of the Japanese Civil War; they used their positions as advisers to the Prime Ministers of the three to provoke them into going to war with each other.
- Mythology Gag: When Build and Cross-Z fuse, we hear blowing wind - the exact sound effect for it in Kamen Rider Double with its many windmills. Double, of course, also being about two heroes who become one Rider.
- No Name Given: Unlike Evolt and latter Killbus, the three other members of the Blood Tribe aren't named, only ever being called by their hosts' names.
- Non-Serial Movie: Averted. It takes place between episodes 45 and 46 of Build and is even built up at the end of episode 45.
- Power Creep, Power Seep: In his debut cameo, Zi-O is IMPOSSIBLY overpowered, appearing in a massive battle between many Riders and their biggest foes, up to and including some Big Bads in their final One-Winged Angel forms, and casually destroys all the villains in one attack, sending the Riders flying. He doesn't get anywhere near that level of power until much later in his own series.
- Villainous Rescue: Evolt shows up to take Sento away right before he can be killed by Kamen Rider Blood.