Houtarou is summoned to a parallel world by Houou Kaguya Quartz to protect it from the evil Hundred. Kaguya seeks power from past Kamen Riders and wants to make Houtarou "gorgeous" to gain his help.

Houtarou is suddenly transported to a parallel world. Awaiting him is a young man named Houou Kaguya Quartz who summoned him using that world's technology, the Aurora Curtain System. His favorite phrase is "Gorgeous" and he protects the world from the clutches of the evil organization called "Hundred". What's more, the person following Kaguya is a butler named Butler, who looks exactly like Houtarou's friend Ryo Kajiki. Kaguya gathers the power of past Kamen Riders who exist in parallel worlds in order to fight against the Hundred. However, unlike the other Kamen Riders, he seems unable to gain power from Gotchard, who is "not gorgeous". Kaguya brought Houtarou into his world in order to make him gorgeous.—Johnny Company