- Written by Shogo MutoDirected by Ryuta Tasaki
In the present day, Sento Kiryu, a genius physicist who suffers from amnesia, becomes a researcher at Touto Institute of Advanced Matter Physics, working on the Pandora's Box. Unbeknownst to his new co-workers, he is also Kamen Rider Build: a hero that hunts down the monsters known as Smash.
He does so in hopes of regaining his memories - Smash are the result of human experimentation by an unknown party, and if his uneasy dreams of being experimented on are any indication, they may be the same party that were responsible for Kiryu's memory loss.
Unfortunately, while Build is able to turn Smashes back to human form, they don't retain their memories of their captivity, so he's out of concrete leads. This changes when Ryuuga Banjo - an ex-pro fighter serving a sentence in prison for murder - escapes and gives off a Smash reading. Catching up to him, Kiryu realizes that this man may be the key to his memories - Ryuuga, while in prison, was also abducted and experimented on by the unknown group, but managed to escape during the procedure.
- As You Know: The episode starts with Gentoku Himuro expositing to Sawa about the Skywall disaster, and how it resulted in the show's setting.
- Big Damn Heroes: Build debuts while saving Sawa's bacon from the Needle Smash.
- Delayed Reaction: After Gentoku proposes a night-long "interview", Sawa walks with him for a short distance before she stops with a Big "WHAT?!".
- Didn't Think This Through: Sento showcases his newest invention, Machine Builder, while in a cafe,and almost drives off to work on the spot.
- Face Doodling: Misora drew on Kiryu's face while he slept after defeating the Needle Smash. He retaliates by writing mathematical formulas on her face when she drops to sleep after purifying Needle's Full Bottle.
- Rewatch Bonus: At the end, Sento pokes fun at Ryuga for having his fly open the entire time, much to the latter's embarrassment. If you rewatch the episode, you will notice that, indeed, his pants were unzipped ever since he met Kiryu.
- Screw This, I'm Outta Here: The man with the earring, Shimizu, runs away as soon as he hears Guardians incoming.
- Take the Wheel: Sento tells Ryuga to drive the Machine Builder, as he needs to protect them from the Guardians shooting at them.
- This Is Gonna Suck: Kiryu has this reaction when he decides to help Ryuga, since this results in Build becoming a fugitive from the Touto government.
- Vagueness Is Coming: At the end of the episode, Night Rogue appears off in the distance, standing on the Skywall, looking on as Sentou and Banjou make their getaway, and says:
- Night Rogue: The war has begun...
