[spoiler]I'll try to explain it as best I can. The cards allow them to either become said Riders (aka Keira), summon said Riders (aka Kara), and access their weaponry and abilities. Their belt and gun used to access those abilities can overheat or be destroyed, reverting them to their fists and kicks. Kara has the powers of Kamen Rider Diend, and Keira has the power of Kamen Rider Decade. Kamen Riders in general is a show created in Japan that began in 1975, with Kamen Rider Ichigo. They've had little breaks here and there, and the show is still continuing to this day, and in 2020, will end up reaching its 50th anniversary. Often (especially during the movies), they fight an evil organization named Shocker, which consists of evil minds and their main soldiers, wannabe Mexican wrestlers. (I'm dead serious.) If you need to elaboration on anything more specific, or if you want more information, then go to the Kamen Rider Wikia, or just ask me. I will probably copy and paste this for anyone else to know, if they ask. 🇯🇵 [/spoiler]