|“How did you know if you freed it from captivity, it would let us go?”|
“Because no one deserves to be held captive. Not even a monster.”
|— Wu and Zane, "The Last Voyage"|
The Leviathan is an enormous sea creature native to the Endless Sea. It resembles an octopus, apart from having three snake-like eyes at the tip of one tentacle.
The Leviathan was captured by Samukai in order to guard Dr. Julien in the lighthouse and chained to the bottom of the ocean. Shortly after the ninja arrived at the lighthouse, the creature investigated the tower, but the scientist was able to conceal their presence from the creature.
Later, the Leviathan attacked the Destiny's Bounty when it attempted to escape the island. The ninja were unable to escape the beast's tentacles, but Zane noticed a great chain binding the Leviathan to the seabed. Diving underwater, the White Ninja used a group of nearby Starteeth to destroy the chain—moments later, the freed Leviathan released the Destiny's Bounty. As both the ship and the creature left the island, Master Wu asked Zane how he saved them, to which Zane replied that he had realized that the Leviathan was just as much a prisoner of the island as Dr. Julien had been.
Dwelling in the waters near the Tomb of the First Spinjitzu Master, the Leviathan noticed the ninja traveling within R.E.X. Disregarding its prior gratitude in favor of a meal, it took chase after them, attacking R.E.X. and cracking the windshield with its tentacle. Outmaneuvering the beast, R.E.X. managed to swim through a small hole in a stone formation that the Leviathan attempted to follow in, getting trapped in the process due to its large size and leaving the beast to thrash in frustration.
Traveling along the Dark Island's coast, the Leviathan became exposed to the Dark Matter in the water, causing it to emanate a purple aura. Noticing an arguing Ronin, Jay, Nya, and Sky Pirates near the shore, the beast took advantage of their distraction to swipe up Ronin, intending to devour the mercenary. However, Jay and Nya succeeded in rescuing Ronin, even as the Sky Pirates fled. Summoning his Salvage M.E.C. to his aid, Ronin proceeded to fire at the Leviathan, wounding and scaring it off from the coastline.
- 22. "The Last Voyage"
- 52. "Grave Danger"
- Legendary Ninja Battles (non-canon)
- The Leviathan is based on the mythical creature with the same name.
- Despite the message at the end of the Leviathan's debut episode the creature is not a monster or a villain, it has had been framed as one in all subsequent appearances.