The Dekarangers must deal with a mysterious undercover agent from another planet while trying to save her world and Earth from one of the universe's toughest Alienizer gangs.

A lonely schoolboy discovers a block of wood carved into the shape of a human head. Seeking companionship he and the puppet-doll become best playmates. Soon things begin to change and the situation goes from innocent to downright sinister.

Arata Kagami seeks to get the Hyper Zecter just like Souji Tendou, so he tries to emulate Tendou. Once he realizes that he has to be himself, the Hyper Zecter appears and allows him to transform into Kamen Rider Gatack Hyper Form.

In 1999, an enormous meteor crashed onto Earth carrying extraterrestrial creatures known as Worms within it. These creatures took on the identities of real humans and then killed them. In order to counter this new threat, ZECT was formed, who in turn created the Masked Rider System to combat the Worms. The battles lasts over seven years, depleting Earth's resources and turning it into a barren wasteland. By present time, power struggles in ZECT have caused a new group, known as Neo-ZECT, to be created. Souji Tendou, a man weilding the Kabuto Zector, decides to sell his power to either ZECT or Neo-Zect for unkown reasons.