Kai

Kai is the ninja of Fire.

Background/Story
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Kai once worked as a blacksmith with his sister Nya.

Attack on Four Weapons Blacksmith Shop
When the Four Weapons Blacksmith shop was attacked by Samukai and his skeleton army, Kai attempted to defend it with some samurai armor he made. The armor was slow and clunky however, and he was soon subdued, and would have died were it not for the quick action of Sensei Wu. Wu then told Kai about The First Master of Spinjitzu and his two sons who fought over the four Golden Weapons, explaining that Kai's father was entrusted with the map.

Training
Sensei Wu took Kai to the Mountains of Impossible Height in order to train him to be a Spinjitzu master so he could save his sister and the whole of Ninjago. During his training, Kai had to learn patience and how to harness the "fire" inside of him. This training consisted of running a course before Sensei Wu finished his tea. Kai accomplished this after several days by knocking the teacup out of Sensei's hands when he was about halfway through the course with his wooden training sword. He then told Kai to get some rest, and that his final test would come in the morning.

Meeting the other ninjas
Later that night, while Kai was pondering Sensei's training and brushing his teeth, he was set upon by three black-suited ninjas. Kai was able to fend them off for a while, disorenting them on the training course. Before they could fight much longer, however, Sensei Wu came out and told them all to stop, at which the three ninjas revealed themselves as more of Wu's students. Wu used Creation to give each of the ninjas a suit that matched their elemental properties, and introduced them to each other. He then told them what they needed to do to defeat Lord Garmadon. Cole interjected and asked if they were still to learn Spinjitzu first. Sensei Wu told them that they each already knew it, but it must be unlocked at the right time. Then Wu said that they would take the horse carriage to the Caves of Despair, the location of the first Golden Weapon, The Scythe of Quakes.

Unlocking Spinjitzu
At the Caves, Kai ran ahead of the other ninjas while Cole was formulating a plan. The other three ninjas chased after him, and caught up to him just before the chamber where the Scythe was housed. Jay accidentally revealed their position to the skeleton army digging for the Scythe, and they were soon in a battle. After Jay discovered the key to unlocking his Spinjitzu, Kai and the others were not too far behind. They used it to drive off the skeleton army, after which they discovered that they had bigger problems, namely, the weapon's guardian, the Earth Dragon. Kai happened to be holding the Scythe at the time, and decided that the only way out was to use it, contrary to Sensei's instructions. After escaping, Kai was strictly repremanded by Sensei Wu, and they went onward toward the next weapon, The Shurikens of Ice.

The Tornado of Creation
While on their way to the Frozen Wasteland, the location of the Shurikens, Sensei Wu told the ninjas about the most powerful move in Spinjitzu, the Tornado of Creation. Kai began to attempt it, but was stopped by Sensei Wu, who explained that it could have disastrous concequences if done incorrectly.

The Shurikens of Ice and the Nunchucks of Lightning
When the ninjas arrived at the Frozen Wasteland, they discovered several skeleton warriors frozen in ice, and deduced that they had been the second people to get there. When they discovered the Shurikens suspended from the celing, they lifted Zane up to grab them. When he did, a block of ice formed around him, and the Ice Dragon guardian awoke. The ninjas used Zane as a sled to escape, and went to the hiding place of the Nunchucks of Lightning, the Floating Ruins. On top of the chain, Jay found the Nunchucks, as well as the Lightning Dragon. As they were being chased by skeletons, the ninjas used Jay's wing-glider invention to leap off the chain and get away to the Forest of Tranquility.

Shadows
While they were sleeping that night, Kai thought he saw his sister Nya. He got up and chased her to the Fire Temple, where he discovered that it wasn't really Nya, but a shadow deception created by Lord Garmadon. His sister was in the Fire Temple however, only suspended over a pit of lava. Kai had to remove the Sword of Fire from its pedestal to cut the chain and save his sister, which was Garmadon's plan all along. He possesed Kai's shadow, and used it to defeat him. The shadow couldn't be hurt by Kai, but Kai could be hurt by the shadow. Garmadon made multiple copies of the shadow, which made quick work of Kai, and obtained the Sword. All would have been lost if Sensei Wu hadn't intervened at that moment, using his own shadow to defeat Garmadon's shadow clones, regaining the Sword. Garmadon then decided to awaken the Fire Dragon, who guarded the sword. The dragon blocked the entrance to the temple, which meant it would be easy for Garmadon to bring the other three weapons to the temple and unite them there, as he had ambushed the other ninjas. Wu then sacrificed himself to go to The Underworld, in order to keep the weapons apart. Kai and Nya then discovered that the Dragon only wanted to protect the Sword, and the ninjas used the guardians to go to the Underworld to help Sensei Wu.

Appearance
Kai wears a red ninja outfit, and has brown, spiky hair. He usually has a very determined look on his face. His Minifigure also has some scars on its face.

Personality
Kai is very tempestuous, and often leaps into things before he thinks. He would leap into a lake before checking to see if there's fire in it. Really, he hopes there is, because he wants to fight it.

Weapons
Kai currently uses the Sword of Fire, but once wielded a normal katana.

In his spinner sets, Kai would also use a double bladed dagger, a flail, a double scythe, a spear, and a golden katana.