Kamen Rider Build, Episode 39: "The Unstoppable Genius"

[Toku Prime]

Behold the king on his throne of bottles
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This week: Takumi has to learn the value of friendship, Seito finally goes with a standard invasion plan, Takumi gets his own transformation sequence and roll call announcement rather than using Sento's, Takumi and Sento finally mentally merge into one complete person, and the final form finally debuts.