The story
The year is 2257. Earth, now peaceful, is a utopia. No disease, no fighting. Human life is perfected, everyone is happy.
Though peaceful, the countries still ruled themselves. Some were more paranoid than others, and began secretly training some people in the ways of combat, usually from a very young age. These people would defend their country, if ever a time came for war.
The coming of age test for these men and women was a simple concept: The day they were capable of defeating their teacher in battle, they were awarded a medallion to symbolize their passage to adulthood. The test could be taken any time they chose, and could only be tried once a year.
The medallions themselves were ancient relics. No one has successfully duplicated one, nor been able to make a new one from scratch. They have mysterious powers, and these powers are directly tied to the medallions themselves. No medallion, no power. The medallions are engraved with a single word that describes their power. (For example, a medallion that gave its wielder elemental control over fire would be engraved with the word "Fire")
Though the story starts before all this, a great war does eventually break out, and the medallion wielders are blamed for it and shunned. Having no where else to turn, they stayed together and formed their own group of outcasts.