- Written by Shogo MutoDirected by Shojiro Nakazawa
Sento: Kamen Rider Build, also known as the genius physicist Kiryu Sento, pursued the truth behind Katsuragi Takumi's murder in order to clear Banjou Ryuga's name. It was thought that everything had been buried in darkness with the destruction of Faust...
- Batman Gambit: According to Sento, it seemed as though Blood Stalk could read his movements as Build as if he already knew about his forms and what the FullBottles in his possession could do. In order to verify his suspicions, Sento made Misora secretly purify what would become the Octopus FullBottle to test if Blood Stalk really was Soichi, as there was no way he could have known about the tenth Best Match, OctopusLight.
- Continuity Nod: In the flashback, the Build Driver doesn't announce the Rabbit and Tank Bottles as a Best Match. Sento had previously said it didn't have that function at the time and that it was something he added later.
- Sneaky Departure: Villainous example. Soichi tried to escape with the 20 FullBottles and Pandora's Box and Panels while the gang was sleeping, but Sento was waiting for him in the restaurant to confront him.
- The Reveal:
- According to Nabeshima, Blood Stalk was the one that killed Takumi Katsuragi, and Blood Stalk's true identity is the astronaut who caused the Sky Wall Incident.
- In addition, it was said that twenty bottles were needed to operate Pandora's box, and with the sixteen or so bottles purified by Sento, plus Faust's remaining four or so, we're at our fated number.
- Villain Forgot to Level Grind: Discussed. According to Blood Stalk, the Hazard Levels with a Transteam Gun always stays constant while a Kamen Rider's Hazard level will always grows, meaning that they will eventually become Weak, but Skilled in comparison to the Kamen Riders who will surpass them. It's up to how the Transteam Gun user grows in experience that gives them the edge.
- Wham Episode: A lot of revelations are revealed, but the biggest one is the Blood Stalk is Soichi Isurugi!
