GiGi Armlet

GiGi Armlet (ギギの腕輪) is a mysterious O-Part of the Incas that was created 120 years ago as one of two keys (the other being the GaGa Armlet) that would allow the user of the two to rule the world with Incan super science. The GiGi Armlet serves as Amazon's power source along with being the only thing keeping him alive. Grafted unto his left arm, Daisuke is originally unaware of the Armlet's true power until he found the Quipu that revealed it.

Kamen Rider Decade
In the A.R. World of Amazon, the GiGi Armlets remains cosmetically the same as the original while the GaGa Armlet is golden. A traveler named Daisuke Yamamoto wears it, aware that his life is in danger if it is removed from him. After Dai-Shocker invaded his world, he met Tsukasa's group and helps them escape the monsters and the townspeople. Trying to befriend a young boy named Masahiko, he ends up loosing his armlet when the boy was tricked by Dai-Shocker into stealing it from him. Acquiring the GiGi Armlet, the leader of the Dai-Shocker protectorate of Geddon, the Ten-Faced Demon Llumu Qhimil, achieves the complete ancient Incan power with his GaGa Armlet, allowing him to convert loyal vigilantes into monsters. Realizing Dai-Shocker's deception, Masahiko stole the GiGi Armlet from Llumu Qhimil and gave it back to Daisuke, allowing him to transform into Amazon Rider once more. With the unexpected participation of Daiki Kaito, who stole the GaGa Armlet from Llumu Qhimil, Tsukasa took the GaGa Armlet with his Attack Ride before using the Amazon Final Attack Ride card to grant it to Amazon, allowing him to use both GiGi and GaGa Armlets to destroy Llumu Qhimil with the Super Big Slice.

All Riders vs. Dai-Shocker
Daiki Kaito (Kamen Rider Diend) was late to the Rider Battle tournament, only participating in the final battle, as, being a treasure hunter, he was busy stealing the GiGi Armlet from Amazon, who was defeated by Decade in the Rider Battle. As the Kamen Riders of the past took their leave from the World of Decade after the battle between All Riders and Dai-Shocker, Diend gave the GiGi Armlet back to Amazon, who was grateful and acknowledged Diend as a friend.

Trivia

 * It was stated that the GiGi Armlet is Amazon's power source and the only thing keeping him alive, however, in both Kamen Rider Decade: All Riders vs. Dai-Shocker, Amazon somehow not only survived, but still managed to transform into his battle form in the movie (although this could be explained by saying that the Amazon in the film is a different Amazon from the Showa TV series) without the GiGi or GaGa armlet.