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

The Unstoppable Hazard (ハザードは止まらない Hazādo wa Tomaranai) is the twenty-first episode of Kamen Rider Build. This episode properly showcases the abilities of Build's RabbitTank Hazard Form after its brief appearance at the end of the previous episode. Also debuting are Build's RoseCopter Form and RoseSoujiki Trial Form, and the Unicorn, Turtle, Spider, Kabutomushi, Tora, Kujira, Kirin, Hachi, Same, Watch, Reizoko, Camera, UFO, Jet, and Senpuki Fullbottles, as well as a tease of Build's TurtleWatch Best Match. It also features the death of Aoba.


Fighting with the forbidden item, the Hazard Trigger, has transformed Sento into a dark version of Build, known as a “Hazard Form”. If he continues to fight using the Hazard Trigger, according to Katsuragi’s words, he will lose his sense of self. Sento is using the same technology the enemy has been using on himself! But Build loses consciousness during the fight. And then, Build stands before the Hokuto Trio as he decides to finish his fight against them…


to be added


Guest Casts

Suit Actors

Forms and Collectibles Used


  • Bottle used:
    • Build
      • Biotic: Rabbit, Phoenix, Rose, Turtle
      • Abiotic: Tank, Soujiki, Helicopter, Watch
      • Other: Hazard Trigger
    • Grease
    • Blood Stalk
      • Biotic: Cobra
      • Abiotic: N/A
    • Castle Hazard Smash
      • Castle
    • Stag Hazard Smash
      • Kuwagata
    • Owl Hazard Smash
      • Fukurou
  • Form used:
    • Build
      • RabbitTank Hazard Form, PhoenixSoujiki Form, RoseSoujiki Form, RoseCopter Form, TurtleWatch Form (off-screen), RabbitTank Form


  • Jelly used:
    • Cross-Z Charge
      • Dragon
    • Grease
      • Robot


Second Rose Body

A second Rose Halfbody

  • Before activating RoseCopter, the Rose Fullbottle is set back into the Driver as if Build didn't assume RoseSoujiki and the Snap Ride Builder part for the Rose Halfbody wasn't clear.


RoseCopter CS
  • Closing Screen Fullbottles & Sclashjellies:
    • Kamen Rider: Build
    • Fullbottles:
      • Biotic: Rose
      • Abiotic: Helicopter
  • Count at episode end
    • Bottles in Build's possession:
      • Biotic: Rabbit, Taka, Panda, Kaizoku, Phoenix, Wolf, Unicorn, Rose, Turtle, Kabutomushi, Kuma, Dog, Spider, Tora, Kujira, Shika, Kirin, Penguin, Obake, Hachi, Sai
      • Abiotic: Tank, Gatling, Rocket, Syoubousya, Densya, Light, Robot, Smapho, Keshigomu, Helicopter, Watch, Camera, Televi, Mic, Reizoku, UFO, Jet, Pyramid, Senpuki, Sukebo, Magnet, Sensuikan, Dryer
      • Other: RabbitTank Sparkling
    • Bottles in Cross-Z Charge's possession:
    • Bottles in Grease's possession: Kuwagata
    • Bottles in Night Rogue's possession: Bat
    • Bottles in Blood Stalk's possession:
      • Biotic: Cobra, Gorilla, Ninjya, Harinezumi, Lion, Octopus, Same
      • Abiotic: Diamond, Comic, Soujiki, Bike
    • Bottles in Castle Hazard Smash's possession: Castle
    • Bottles in Owl Hazard Smash's possession: Fukurou
    • Jellies in Cross-Z Charge's possession: Dragon
    • Jellies in Grease's possession: Robot
  • In the opening sequence for this episode:
    • Grease replaces the scene with two of Build's forms.
    • Cross-Z Charge replaces the scene with Cross-Z.
    • Build changing from RabbitTank to RabbitTank Sparkling replaces the scenes with GorillaMond and HawkGatling.
  • The title of the episode has two meanings:
    • Hazard form is unstoppable, the power of Hazard Form is too strong that it cannot be stopped by others
    • Hazard form will not stop fighting, Sento cannot control Hazard Form to stop it from destroying every enemy
  • When Sento revisits the location of Aoba's death, the flowers he places there are purple hyacinths. Purple hyacinths are a symbol of sorrow, as well as asking for forgiveness.
Case of Bottles…that could've sounded better
  • When Isurugi presents Sento the case of Fullbottles, despite being on Seito- and Hokuto-colored Panels, the assorted Bottles are not arranged by district, Best Match, or even biotic/abiotic. This may either be an error by the prop department or be Isurugi trying to make Sento find the Matches on his own.
  • This is the first episode since it's debut that Sento does not assume his RabbitTank Sparkling Form.

DVD/Blu-ray releases

External links


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