Yuichi Saito is Miyuki Tezuka's friend and the chosen owner of the Card Deck that Tezuka eventually took up.

He was an excellent pianist, who had lost his ability to play when a mugger (later revealed to be Takeshi Asakura) broke his hands. Shiro Kanzaki later appeared before Yuichi to offer the restoration of his hands by becoming a Rider, but Yuichi refused and was eaten by the monster GuldThunder as a result. This led to his friend Tezuka taking the Card Deck, contracting Evildiver and becoming a Rider to avenge his friend by ending the Rider War. 

Rider Forms:
-Kamen Rider Blade

This other Rider was named Kamen Rider Blade, preceding the official Kamen Rider Blade.

Contract Monster:
-GuldThunder