The ruler of the evil Phantom Empire, Queen Mirage, begins her invasion on Earth using an army of Choiarks and powerful monsters called Saiarks. All across the world, Pretty Cures are dispatched to fight against the Phantom Empire threat. Hime Shirayuki, a princess from the Blue Sky Kingdom, which was taken over by the Phantom Empire, joins the fight as a Pretty Cure named Cure Princess, but always finds herself running away scared. Given a Crystal of Love by the Spirit of Earth, Blue, and told to seek out a partner to fight alongside her, Hime goes to the city of Pikarigaoka and randomly throw the crystal in the air, deciding to partner up with whoever it lands upon. This person turns out to be Megumi Aino, a kind-hearted girl always looking to help others, who is recruited by Hime to fight by her side as Cure Lovely.

"Mirror World" exists symmetrically beyond an invisible mirror in space, and an exact copy of our human world, where only monsters can dwell. Evil monsters frequently cross the mirror and attack our world. Only Kamen Riders who make a contract with a specific monster and obtain special power from it, can enter "Mirror World" and fight against evil monsters with the help of an "Advent Card."

Shinji Kido, a journalist, contracts with a dragon and becomes Kamen Rider Ryuki. He fights a fierce battle with evil monsters. Many Kamen Riders appear one after another and fight to satisfy their own aims. However, only one Kamen Rider can outlive others. Thus, it is their fate to keep fighting to the last man.