KAi

Kai is the current Elemental Master of Fire, Nya's brother and he is the son of Ray and Maya. He and his younger sister were blacksmiths in their father's blacksmith shop all their life until they met Master Wu. With Master Wu's guidance, Kai learned Spinjitzu and discovered his other teammates, Cole, Jay and Zane with whom he embarked on many adventures; battling the likes of the Serpentine and the Stone Army.

After Zane's sacrifice to destroy the Golden Master the Ninja parted ways before reuniting to go rescue Zane on Chen's Island. There, Kai grew closer to Skylor, one of the tournament contenders, as they competed in the Tournament of Elements. Ultimately, he allied with the other Elemental Masters to defeat Chen's Anacondrai warriors. After the war ended, Lloyd was possessed by Morro, who escaped the Cursed Realm and released a legion of ghosts. Kai and the Ninja battled Morro and his forces before the Cursed Realm was destroyed.

The Ninja found fame after saving Stiix, but when Nadakhan returned with the Sky Pirates, Kai was the first of the Ninja trapped in the Sword of Souls. Jay freed him and reversed recent events with his final wish. On the Day of the Departed, Kai and Nya fought a revived Chen, who they defeated once more. When the Time Twins returned to Ninjago, Krux tried to convince Kai that Kai's parents were traitors. Kai and Nya reunited with their parents and stopped Krux and Acronix from changing the future. They managed to track them through time and stopped them before Wu sent Kai and Nya back to the present, while Wu ended up lost in the time.

Kai and the Ninja later watch over Princess Harumi after she lost her adopted parents. They later discover that she secretly is the leader of the Sons of Garmadon and wants to resurrect Lord Garmadon. Despite the Ninjas' efforts, Harumi successfully resurrects Garmadon, and shortly after, Kai ends up marooned in the Realm of Oni and Dragons with Cole, Jay, Zane, and the de-aged Wu. Kai and the Ninja help save the various dragons from the Dragon Hunters and help the now-teenage Wu regain his confidence and memories. After Iron Baron is defeated by Firstbourne, Wu reclaims the Dragon Armor, in turn allowing them to return to Ninjago. Upon returning, along with his fellow Ninja, he takes down Garmadon's Colossus while Lloyd defeats his father, restoring peace to Ninjago once again. Afterward, he along with the other Ninja attend the celebration and Kai and Skylor share a moment. When the Oni finally invade, the Ninja team up with Lord Garmadon, and Kai and the rest of the Ninja fight to defend their home. Kai used his blacksmithing skills to reforge Golden Weapons, using the Golden Armor, and later defeats the Oni by using the Tornado of Creation with the other Ninja, Wu, and Garmadon.

Months later, Kai and his friends fight against Aspheera and her Pyro Vipers after accidentally releasing them from their tomb, and Aspheera took away Kai's power, making Kai think that he can't help. After Zane is banished by Aspheera's sorcery, he and the remaining Ninja send themselves to the Never-Realm to rescue him, a land ruled by the Ice Emperor. While Lloyd went to find Zane, Kai and the others protected the Ice Fishers of Great Lake, who call Kai the Fire Maker after he relights the Hearth Fire and regains a fraction of his power. After failing to prevent Boreal from freezing the village, Kai makes up for his loss by regaining his full powers in time to destroy the Ice Dragon, discovering that Zane is the Ice Emperor. With Zane having managed to return to his senses and freeing the Never-Realm from its eternal winter, the team reunite together and use Traveler's Tea to head back to Ninjago.

Sometime later, Kai and the other Ninja enter the virtual world of Prime Empire, when the legendary arcade game resurfaces and hundreds of gamers are zapped into it. Due to his recklessness, Kai was the first to lose all but one of his lives, and later, he and Cole sacrifice themselves in a race, allowing the rest to win. Eventually, Jay was able to help Unagami and Milton Dyer make amends, releasing Kai and the others trapped in the game.