[KamenRanger1997]

While it's not about the other riders, I did come up with an idea for a Saber/Zero-One movie: Swords of Life and Death

A villain named Gene shows up, injures Yuri and takes the Kougouken Saikou. He reveals that the Saikou and Ankokuken Kurayami are weaker forms of the true first two Seiken; the Inochiken Hajimari, which has the power of life, and Shiken Owari which has the power of death. Gene uses the Hajimari to become Kamen Rider Genesis and control all life on earth.

The only ones not affected are the other Seiken welders and Humagears. Genesis sends Zero-One, Vulcan, Valkyrie and Thouser to fight the Saber Riders. Izu frees Aruto through his connection to Satellite Zea.

After some research, Yuri discovers the only way to defeat the Hajimari is to use the Owari, and the only way to turn the Kurayami into the Owari is to expose it to a being of pure destruction. With no other choice, Aruto convinces Touma to bring the Kurayami to Azu, who becomes fully possessed by Ark and turns the sword into the Owari and transforms into Kamen Rider Mortem.

The other swordsmen hold off the mind controlled Riders while Saber, Zero-One, Zero-Two and Mortem defeat Genesis. Mortem then turns on the others, wanting to use the Life and Death swords to annihilate humanity.

Azu connects Zea to the computers in Northern Base and creates a Saber-themed Progrise Key for Aruto and a Zero-One-themed Wonder Ride Book for Touma. With their new forms, the two heroes defeat Mortem, destroy Azu and Ark disappears once again.