- Written By:Shogo MutoDirected By: Satoshi Morota
Sento: A wars erupted between Touto and Hokuto over the immense energy within Pandoras Box. Kamen Rider Build, Kiryu Sento, attempts to stop Hokutos invasion, but is forced to use a forbidden item in order to stop Banjo from going berserk
Tajimi: Is it true that forces from Touto are headed towards Hokuto?
Sento: Hokutos Prime Minister Tajimi! Im afraid Im unaware of any
Tajimi: Do you really think I would fall for that?!
Sento: Well manage something in episode 21!
- Armor-Piercing Question: Sentos Build Drivers signature Are you ready? line before the transformation cuts deep into his trauma as it reminds him of what he did earlier in the episode and of the monster that is RabbitTank Hazard. Despite his fears, Sento chooses to respond with the usual Henshin and armor up.
- Batman Gambit: Soichi proposes that Sento can potentially bring himself into top form in time for the proxy battle, and ideally, raise his Hazard Level to the point where Sento could even handle using the Hazard Trigger without losing himself, but only if he was willing to fight again. Sento, who wants to end the war as painlessly as possible, resolves to stand up and try to find a way so that he can succeed.
- Break Them by Talking: Soichi goes on mocking Sento's desire to protect everyone and reminding him of things he doesn't want to think about because they hurt him for so long Sento snaps and charges at him in blind fury just to make him shut up.
- The Chains of Commanding: Near the end of the episode, Soichi decides to talk to Sento to try and get him to participate in the proxy battle, citing that if Sento does not fight, Ryuga will have to fight in Sentos stead despite being weaker than Kazumi as is, and that if Kazumi wins then there will be hell to pay for Ryuga being unable to protect Touto.
- Dark Reprise: ARE YOU READY?! READY? Ready? ready?
- Evil Mentor: Soichi trains Sento in using FullBottle to their full potential to prepare him for his fight with Kazumi that will decide the war's outcome.
- Get a Hold of Yourself, Man!: Sento receives this from Soichi of all people at the end of his Break Them by Talking speech. He is reminded that he wanted to fight for justice and protect people and to continue do so, he has to get up and fight.
- It's All My Fault: Two examples:
- Sento undergoes a worse Heroic BSoD than the one he had when he realized he was Takumi Katsuragi, becoming an Empty Shell and completely losing his conviction that he would protect everybody as Build because he ended up taking a life due to using the Hazard Trigger.
- Ryuga blames himself for not being able to control himself while using the Sclash Driver and being directly responsible for Aobas death because Sento used Hazard Trigger to try and stop him. Also, he promised to protect Sento from suffering anymore and failed.
- Not So Stoic: In a very subtle way, in the scene where Kazumi was telling Sento about the arranged proxy battle, his hand that was holding Syuuya Aikawas dog tag was visibly shaking against Sentos arm despite his cold professionalism.
- Reality Ensues: Even though Sento became unwilling to fight anymore and Prime Minister Himuro relinquishes the Kamen Riders from their service to protect Touto, this doesnt stop Hokutos military conquest. Even with Taizan back in the reins, he could only get Prime Minister Tajimi to minimize the casualties of the war by agreeing to a one on one proxy battle using the Kamen Riders as their representatives.
- Silly Rabbit, Idealism Is for Kids!!: Both Kazumi and Soichi tell Sento he can't protect everyone, because that's not how things work. The difference is that while Kazumi presents it as fact of life to be aware of, Soichi mocks Sento for believing it.
- These Hands Have Killed: Sento develops PTSD as a result of his actions. When he goes to pay respects to Aoba at his death site, he has a hallucination of Aoba hating him, and the guilt becomes more than what Sento could bear to the point where Sento begs Kazumi to just beat him up until Kazumi is satisfied.
- The Un-Reveal: Soichi brings twenty FullBottles with him so that Sento could train himself back into shape and become a better fighter. However, the end of the episode skips one week ahead to when the battle begins, which means the viewer doesnt get to see all of Sentos training or the forms he can use, like TurtleWatch, to promote their focus in the YouTube miniseries.
- War is Hell: Surprisingly enough, the one who prevents things from devolving into a back and forth of people dying on either side of the Kamen Rider sides is Kazumi, who doesnt blame Sento or Ryuga for their actions but also coldly rebukes them, saying that they should not be fighting in this war if they werent ready for what war is.
- Warrior Therapist: Soichi becomes one for Sento to try and force Sento out of his funk in time for the proxy battle, even using a What the Hell, Hero? speech to try and get Sento to stand up for himself.
- Wham Episode: The ruthlessness of Hazard Trigger was portrayed as less Moment of Awesome but more Nightmare Fuel from start to finish and it ended with the death of Aoba which completely broke Sento to the point he's not fighting to protect the last remaining Full Bottles for the sake of Touto and its people. Even the Hokuto Trio stopped being comedic after witnessing one of them dead.
- What Measure Is a Non-Human?: Soichi tells Sento that he and Aoba ceased to be human the moment they were injected with Nebula Gas. Sento didn't kill Aoba, he just broke a weapon.