[806mtson]

Theorising About Kamen Rider Revice Start:
I have just realized why Vice is so different from Ikki: He represents all of the things Ikki had tried to suppress. Think about it: Ikki hasn't had much me-time since he started helping run the family bath house. He gave up on his dream of being a Soccer (Football for you non-Americans) Player to help run it. He has worked so hard to the point where even he believes he is the hardest worker in Japan. The thing is, everyone deserves a break. Especially comparing how his father barely does anything around the bath house. So, you'd think that he would want to take a break. But, he barely takes them, at least on screen. The Most of a "break" Ikki gets is being a Kamen Rider. And even then, he treats the Kamen Rider as a side-gig, to the point where he might cause more people to be harmed. As Ikki is so selfless, Vice is selfish. Vice is the exact opposite of Ikki. Plus, Vice's name, besides meaning "evil" and "secondary", also means "immoral act" and "a bad habit" (like drinking, smoking, overeating, etc), and, of course, letting your vices take control of your life can be dangerous. So, I say that's what the Berserk Form will be: Vice taking over Ikki's Body, possibly with an attachment given to him by the Deadmans. The Deadmans could convince Vice to get the attachment that attaches to the Barid Rex Vistamp to take over Ikki's Body. Now, without Ikki's Oversight, he can do whatever he wants. I think that would be a mini-arc of sorts.
Theroizing End:
Anyways, I don't think that the Build-based Hyper Battle Form will be the Kangaroo Genome. The colors are all wrong on the Vistamp. Build isn't Orange and Green, he is Red and Blue. The Build-based Vistamp has to be Red and Blue. Because the closest-possible color scheme would be HawkRessha, which isn't the basis for the form. The Form in the silhouette is based upon RabbitTank, not something that isn't even a Best Match.
Plus, the Marble-like Eco Armor for the Kangaroo Vistamp is Gray like the Showa Stamps. Not Blue like the Heisei Vistamps. So it feels impossible for the Kangaroo Vistamp to be based upon Build.
Sorry.