|Weapons/Accessories||Sword of Fire|
|Vehicles and/or Gadgets||Blade Bike|
|Occupation||Ninja of Fire|
|Residence||New Ninjago City|
Once, when Kai and his sister, Nya were working the Four Weapons blacksmith shop, they were approached by Sensei Wu, who showed disdain for the weapons they made, claiming that they would be useless in the art of stealth. He also said that they were fit weapons for a samurai, but useless for a ninja. Kai drove him off, but he then disappeared when Kai turned his back. Moments later, a dark cloud appeared over the village, which local farmers were the first to notice. On the edge of a hill, a large vehicle (the Skull Truck) appeared along with many motorcycles, all with skullkin aboard them, notably General Nuckal, Kruncha, and Samukai. The farmers attempted to attack the skullkins, only to run away at the last second. Then, Kai, wearing hand-crafted samurai armour, helmet, and sword, engaged the skullkin in battle, with Nya joining in. Kai was nearly killed by Samukai, only to be saved by Sensei Wu, who reappeared just in time. He was not able to save Nya, who was kidnapped under the orders of Lord Garmadon. Sensei then told Kai the history of Ninjago
After telling Kai the story, Sensei told Kai that his father had a map made by Wu, showing the locations of the hidden Golden Weapons, and also that Garmadon had struck a deal with Samukai, and that Wu was Garmadon's younger brother. Kai at first refused to get involved, until realizing he wouldn't stand a chance against the skullkin on his own. He then trained in Wu's monastery, and, after completing his training, awaited a final test, but is told he had already learned spinjitzu. Later that night, Kai was ambushed by three ninjas, and the ensuing battle causes him to be thrown out onto the training grounds. Kai activated the training course and the obstacles disarmed his attackers. Moments later, Sensei Wu stops the fight, revealing that the three are his other students. Sensei then uses spinjitzu to transform their black costumes into outfits corresponding with their element. The four are introduced to each other: Cole, the black ninja of earth; Jay, the blue ninja of lightning; Zane, the white ninja of ice and a seer with sixth sense; and Kai, the red ninja of fire. Introductions were cut short as Wu announced the search for the golden weapons had now begun.
Ninjago: New Ninjago City
- Strangely, when Kai interacts with Peter Venkman he says that the Ninja "could have used [his] help a while back." (a reference to Ninjago's fifth season, which featured ghosts as the antagonists) However, the dimensions crisis takes place during Ninjago's fourth season.
- Along with Scooby-Doo, Kai is the second Team Pack character to have a line when riding K-9.
- Kai, along with Cole, Sensei Wu, Lloyd and Jay, makes a cameo in beginning of Elements of Surprise. Unlike Cole, who appeared in his tournament attire, Kai, Lloyd and Jay appeared exactly like their toy minifigures.
- In LEGO Dimensions, Kai uses his variant from the first half of 2015 sets and episodes. However, his accessory is the Sword of Fire, which were destroyed in the show before this outfit was introduced.
- In the television series, Kai is voiced by Vincent Tong. In LEGO Dimensions, Kai is voiced by Charlie Schlatter.
- Tong had even commented on a video in YouTube that he wasn't contacted to reprise Kai for the game to begin with. Which is due to the fact the series itself is recorded in Vancouver, British Colombia, Canada, while Dimensions recordings take place primarily in Los Angeles.
- His toy tag is based on his 2015 Ninja of Fire suit, while his Ninja symbol is its main symbol.
- Main article: Kai/Gallery