This article is about a/an episode in Kamen Rider Build.
Red alert WARNING: This episode contains scenes of blood, bloodshed and gun violence. Viewer discretion is advised!

Theory of Conspiracy (陰謀のセオリー Inbō no Seorī) is the twelfth episode of Kamen Rider Build. It features the debut of Build's KaizokuRessya Form, the Kaizoku Hassyar, the return of Masahiro Nabeshima since Episode 4, and Nariaki Utsumi's first transformation into Night Rogue as well as his apparent death before his return 6 episodes later.


Sawa was revealed to be a spy for Namba Heavy Industries! It was her job to secretly collect data on the Kamen Rider system as a military weapon. Thanks to Sawa's info, Sento has become aware of the connection between Namba Heavy Industries' intentions and Faust's mission to reclaim the Pandora Box. Sento manages to unlock a new Best Match in the middle of a fight, however the prospect of Faust being aligned with the Touto government raises an unexpected behavior within Sento...


to be added


Guest Casts

Suit Actors


  • Bottle used:
    • Build
      • Biotic: Kaizoku, Lion (in Build Phone), Ninjya
      • Abiotic: Densya, Comic
    • Cross-Z
    • Night Rogue
      • Bat
    • Blood Stalk
      • Biotic: Cobra
      • Abiotic: N/A
  • Form used:
    • Build
      • KaizokuRessya Form, NinninComic Form


  • to be added


KaizokuRessya CS
  • Closing Screen Fullbottles:
    • Kamen Rider: Build
    • Fullbottles:
      • Biotic: Kaizoku
      • Abiotic: Densya
  • Count at episode end
    • Bottles in Build's possession:
      • Biotic: Rabbit, Gorilla, Taka, Ninjya, Panda, Harinezumi, Lion, Kaizoku
      • Abiotic: Tank, Diamond, Gatling, Comic, Rocket, Syoubousya, Soujiki, Densya, Light
    • Bottles in Cross-Z's possession:
    • Bottles in Night Rogue's possession: Bat
    • Bottles in Blood Stalk's possession: Cobra
    • Bottles in Hokuto's possession:
      • Biotic: Wolf
      • Abiotic: Smapho
  • This is the first episode since episode 1 to not feature the opening credits, the credits instead scrolling over the end of the episode. Coincidentally, the previous season's episode 12 also didn't have its opening credits.
  • From this point on, Ryuga's Rider form is referred to as Cross-Z, a name created and christened by Sento to differentiate him from Build.
  • Coincidentally, the previous series's episode 12 also featured an evil Rider(-like) character murdering someone to hide their secret.
  • Upon the completion of the episode's production, Yuki Ochi was given farewell flowers by the production team to hide his later return six episodes later where he was revealed to be working with Nanba Heavy Industries.
  • This episode marks the 400th episode of the Phase 2 Heisei era Kamen Rider Series.

DVD/Blu-ray releases

External links


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