Long before time had a name, the realm of Ninjago was created by the First Spinjitzu Master, using the four weapons of Spinjitzu. When he passed away, his two sons swore to protect the land and the sacred weapons. However, the oldest, Garmadon, succumbed to the darkness within him when he battled his brother, Wu, in an attempt to steal the weapons for himself, forcing the youngest to strike him down into the Underworld. In the wake of his brother's descent, Wu hid the weapons, giving the map to an old blacksmith friend to hide. With the weapons safe at last, Wu then vowed to recruit the next generation of elemental fighters. Years later, the blacksmith's son, Kai, is on a mission to save his sister from Lord Garmadon's undead Skulkin forces, and is recruited by Sensei Wu along with three other teenage boys to wield the Golden Weapons and defend the world from evil.