A teenage blacksmith named Kai who lives with his sister Nya. Kai works as a blacksmith to sell them as armor. The Skeleton Army comes and prepares to attack the Japanese village. The leader is Samukai and the two generals are Kruncha and General Nuckal (who fight every time in the movie). They attack the city. Kai then gets his armor and fights Samukai, but Samukai gets his bone daggers and throws them at a water tower, causing it to nearly fall on Kai. A ninja master named Sensei Wu saves him using Spinjitzu, which Kai mistakenly calls “twistitsu” when he is mad at Sensei.
Samukai and his army leave with Nya captured by them. Sensei then tells Kai if he wants to save his sister he needs to learn Spinjitzu to defeat the army. Sensei also tells him the story of Lord Garmadon, his brother, who is responsible for the army formation. Kai then trains in the dojo and Sensei brings his other ninja students(Jay, Cole, and Zane) to work with Kai (they accidentally attack Kai when they first meet). They all head towards the earth land, get Cole’s scythe, and leave, narrowly escaping the Earth Dragon.