It was in a modern day world with guns and wars, there was some kind of armed conflict going on.
The story was about seven powerful crystals or gems or rounded stones, each carried by a different person wielding it in a way that suits his fighting:
- One of them had it embedded in his shield, it was green I believe
- One of the characters also carried his stone around and played with cards
- The main protagonist had it in the hilt of his sword I think
In one of the scenes the boy was shown to have been born with the stone in his hand.
By the end of the series they were trying to unite the power of the stones to defeat some kind of enemy.