Medals (メダル), referred to, for clarity, as O Medals (オーメダル), are special coin-like medals that are the center of Kamen Rider OOO’s different powers based on the animal the Medal represents. There are two different types of O Medals: Core (コア) and Cell (セル). Core Medals (コアメダル) are colored O Medals that make up the essence of a Greeed. They can also be used to transform into Kamen Rider OOO or any Combos.
These five types of Core Medals were originally fifty (five sets of ten) created by human alchemists 800 years ago as a means to create artificial life, drawing from characteristics of different animals, forming the core of the Greeed before one Medal in each set was taken. With the tenth medal gone in order to create a ‘desire’ in the nine other medals, the Greeds were created. A sixth set was also created, the Purple Cores, which are made from the antithesis of desire. Later Core Medals were created with current and future technology which seemingly surpass previous Core Medals in power. It is also notable that Foundation X somehow managed to turn Kamen Riders themselves into Core Medals.
Each set of Core Medals comes in a specific color and animal type. Red Core Medals have bird powers; yellow Core Medals have big cat powers; green Core Medals have insect powers; silver Core Medals have heavy mammal powers; blue Core Medals have marine animal powers; purple Core Medals have dinosaur powers; and orange Core Medals have reptilian powers. There are 70 Core Medals total from the series, each three from a Greeed divided in three groupings for the use of OOO: Head, Arms (Torso), and Legs. They have either one, two, or three horizontal bars on their backs, respectively, to indicate which corresponding OOO Driver slot they are compatible with.