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.

Nine universes of the previous Kamen Riders from the Heisei era are merging into one, something that would destroy all the worlds. To prevent this, Tsukasa Kadoya transforms into Kamen Rider Decade and is told that to protect his own world he must travel to all of the other Kamen Riders' worlds (Another Rider's worlds) and eliminate the anomalies in those worlds. Along the way, confronting the mysterious Narutaki and the thief Daiki Kaito, they are joined by Yusuke Onodera of the World of Kuuga and Kivala of the World of Kiva.