Souryuuden (Legend of the Dragon Kings)

Synopsis

The four Ryudo brothers hold an ancient secret - they are descended from the dragons. They have the speed, strength and power of their legendary ancestors - and they're getting stronger. But when pushed to the limit, they become the terrifying, uncontrollable dragons of mythology. These powers have attracted the attention of some powerful enemies - shadowy organizations with unlimited resources and weapons who will stop at nothing to control the brothers. (Source: U.S. Manga)