- Written by Shogo MutoDirected by Shojiro Nakazawa
Sento: Kamen Rider Build, the brilliant physicist Kiryu Sento, has headed to Hokuto to seek out Katsuragi Takumi's mother. There, he learns that Faust was actually founded by Katsuragi.
Ryuuga: Katsuragi was a true genius. Unlike somebody I know...
Sento: You don't know squat. Nobody wants to hear about the Schwarzschild radius and thermal vents on a Sunday morning. I'm playing it down.
Ryuuga: Then how did you make the 4-Panel Ninpo Sword?
Sento: Well, first I bladdat, then phwhee, and then, wham!
Ryuuga: That's just onomatopoeia!
Sento: Geniuses have trouble putting things in layman's terms! What'll happen on Episode 8?!
Katsuragi Takumi was the founder of Faust! Sento and Ryuga are frozen by these words that Blood Stalk just revealed to them. A fearsome power may be at work behind the murder of Katsuragi Takumi. And this is mostly because Build’s lost memories are involved. There is a sign that secret data entrusted to his mother by Katsuragi might be a clue. While talking to Katsuragi’s mother, these two become certain that this data collection exists. The fight between Build and Faust arises once again over the existence of this mysterious data…
- Bait-and-Switch: The viewer is led to believe that the safety deposit box in a Touto bank contained Takumi's research data, but it and the key were a red herring as Takumi left his mother with instructions in case there was a group of people that came to her for his data and she didn't trust them.
- Driven to Suicide: Shinobu Katsuragi, Takumi's father and head of the Mars expedition that brought back Pandora's Box, committed suicide after being harassed from all sides following the Skywall incident.
- Kick the Dog: Gentoku offers a trade with Kyoka Katsuragi, Takumi's mother, to hand over the location of Takumi's research data in exchange for Takumi's will that supposedly contains a heartfelt letter to his mother. She willingly trades a key and safety deposit box number for the letter, only to find that the letter was completely blank and was forcibly transformed into a Smash for her trouble.
- I'm Crying, but I Don't Know Why: Sento tears up after tasting the tamagoyaki made by Kyoka Katsuragi and really likes it despite Ryuga's protests that it's too sweet. He was reacting to the comfort food she served him when he was still her son Takumi.
- It Amused Me: Blood Stalk continues his nebulous agenda by handing over Takumi Katsuragi's research data over to Ryuuga after swiping it himself in response to Ryuuga's rising Hazard Level.
- Turn Out Like His Father: Kyoka believes that Takumi became a scientist out of his father's example, and later as atonement for his father's regrets.
- You Remind Me of X: When Kyoka makes tamagoyaki for Sento and Ryuuga, Sento invokes the second variant of this trope by accidentally reminding Kyoka about how Takumi loved eating his mom's tamagoyaki.
- Wham Shot: "Project...Build...?"
