[Kiwami]

Well this came together beautifully.

So the Gifu Stamp can amplify the darkness within humans for their inner demons to emerge and take form, which kills the host. Vistamps are based on the Gifu Stamp to harness and weaponize that effect, but demons released through the stamps were uncontrollable and harvesting the power of inner demons through a Driver made the demon ate the host's life away.

Then an unwilling subject was infused with cells from the Gifu statue which made the transformation stable, and the first Kamen Rider was a military super solider.

That soldier later cut his heart and demons alongside with it out to escape, settle down and have a family. His three children all share the Gifu cells so they have unique demons as well and can transform into Kamen Riders. Also this is why the Igarashi demons act weird and react to Gifu's slow awakening.

It's a big moment for a Kamen Rider show once the puzzle pieces fit into the big picture and they explain the "Why" and "How", and at this point I want to say Revice is among the best examples for how to do it right.

Also, Kamen Rider Vail's design rules. I though it looked a bit militaristic, turns out that was intentional.