Huntik: Masters of Ninjetti

Huntik is an anime series about a group of teens who become ninjas by night and master a special power called Ninjetti.

Story
Long before time had a name, the First Ninjetti Master raised the island nation of Spinjago using the power of four ancient weapons: the Scythe of Earth, the Nunchucks of Lightning, the Shurikens of Ice, and the Sword of Fire. Weapons so powerful that no mortal can control all their power at once.

When he passed away, he left the weapons in the care of his two sons, but the oldest was consumed by darkness and wanted the weapons for himself. Soon afterwards, an earth shattering battle-of-brothers broke out nearly tearing the land apart. In the end, the  younger brother emerged victorious while oldest one was cast down to the depths of the Underworld.

Peace and prosperity had returned to Spinjago, but knowing his brother or anyone who would dare use them for evil, the younger brother took the Golden Weapons and scattered them to far corners of the island and with them placed a guardian dragon to protect them.

Many years have passed since then, and the older brother has returned along with an army of skeleton warriors and are ever searching for the Golden Weapons. Now to old to face his brother again, the youngest son has assembled four teens as his apprentices to find the Golden Weapons and the defeat the darkness.

They are ordinary high schoolers who are each struggling with their own problems. They must now put their problems aside, train their new ninja skills, deafeat the forces of darkness, and become the Masters of Ninjetti!