Kai is a ninja from NINJAGO, not the ninja theme . He's Nya's brother. Kai is the Blacksmith's son in which Kai became a blacksmith before he became the Ninja of Fire. Before his father died or dissapeared, his father hid the map to the Four Golden Weapons. Also, Kai is now running his father's shop, The Four Forges, along with his sister, Nya. Before his sister was abducted by Garmadon's army, Sensei Wu commented on their Samurai Armor, and he said "Strong armor, but slow for a ninja."Kai's descrpition on LEGO.com:
Weapon of choice: Sword Elemental color: Red Strength: Attack
Kai is like fire; he's wild and dangerous. He's quick to act, quick to attack, and quick to get into big, big trouble. He's very good at finding trouble.
Kai can't wait for anything. He jumps headfirst into a pool before checking to see if there's fire in it. He hopes there is…he wants to fight it. Good thing Kai burns.