Kai

Kai is the Red Ninja, the Elemental Master of Fire and Nya's elder brother. Kai and his younger sister, Nya, continued to work as blacksmiths in their deceased Kai and Nya's Father's shop. With the help of a wise sensei,Wu, Kai learns Spinjitzu and discovers his three other teammates, with whom he embarks on many adventures with as they battle the Serpentine and eventually The Great Devourer.

Kai and the Ninja soon fought the Stone Army in a desperate effort to prevent the final battle, which was soon made all but certain. After Lloyd defeated the Overlord and his father was purified of evil, peace resumed in Ninjago until Pythor returned, aiding The Overlord in becoming the Golden Master and commanding the Nindroid army. The Ninja fought the Overlord and his Nindroids until Zane sacrificed himself, vanquishing the Overlord but seemingly dying in the process. Kai, Jay and Cole were left severely disheartened after this.

When Lloyd attempted to get the team back together, the other Ninja were very reluctant, but when they found out Zane was still alive, they reunited and journeyed to Chen's Island to compete in the mysterious Tournament of Elements. When Chen's true plans unfolded and the competitors of the Tournament allied together, Chen's army was defeated at the Corridor of Elders, but only after Garmadon sacrificed himself. After his father's banishment to the Cursed Realm, Lloyd was looked after by Kai, who became an influence on him. Kai was devastated when Lloyd was posessed by Morro. As an army of ghosts were released from the Cursed Realm, the Ninja battled Morro and his forces at Stiix before the Cursed Realm was destroyed upon The Preeminent's destruction.

The Ninja found fame after saving Stiix from the ghosts, with Kai becoming obsessed with his popularity. However, the Ninja were soon locked away in Kryptarium Prison for crimes they didn't commit. After escaping the prison, the Ninja fought against Nadakhan and Sky Pirates. During their first encounter, Nadakhan trapped Kai in the Sword of Souls, leaving him absent during much of the crisis. Kai was later freed by Jay, and witnessed Nya die after being struck by Tiger Widow venom. Jay then used his final wish to reverse recent events, saving Nya. On the Day of the Departed, Cole accidentally revived the Ninjas' old enemies, including Chen, who attacked Kai and Nya with help from Eyezor and Zugu. Kai and Nya defeated their adversaries before setting off to Yang's Temple, where they witnessed Cole becoming a human once more.