Jei is an enemy of Miyamoto Usagi, who claims that he was sent by the gods to eliminate evil. He intends to kill anyone he believes has evil in their heart, which is basically anyone that isn't under his influence.
Jei is a wolf with gray and black hair, half of which is tied with white material. Dressed in a black kimono. He has sharp teeth and has no pupils nor irises, so it looks as though is was blind. He carries a black yari as a weapon.
Jei appears as the main enemy of Usagi and the Ninja Turtles in a crossover trilogy in the fifth season of the 2012 animated series. Deviating from his model, he has certain mystical powers, including the ability to summon the turtles out of their reality and master the minds of others. His plan is to take possession of the body of Kintaro, a boy born with divine powers, so as to become invincible. The plan, however, is stopped by Miyamoto Usagi, Kintaro and the Turtles, and he ends his (current) life in the abyss of the Temple Mount, where he is thrown down by Usagi and Kintaro.
Jei is first seen just after he murdered a family with Miyamoto Usagi as witness. Usagi berates Jei on how he could do something like that, calling him insane and a demon. Jei claims that his actions were justified, saying that they were infected with evil and the gods revealed their nature to him. As Usagi and Jei do battle, Jei continues to claim that the gods gave him his skill to cleanse this realm of evil, to which Usagi replies that he is the evil one. Just before Jei strikes him down, Usagi asks him who he is, to which he replies "I am Jei, the Blade of the Gods" and then disappears as he is stuck by lightning. He later appears in his own dwelling mystically watching Usagi as he is escorting Kintaro through the forest to the temple palace, believing that the gods have brought Usagi to him again. He decided he needed great warriors to destroy him, and thus performed a magical chant that summoned the Ninja Turtles from across the realms. Jei played a victim saying that Usagi attacked them to get close enough to hypnotize them. He then orders them to hunt down and destroy Miyamoto Usagi, but leave the boy he travels with unharmed, to which the turtles comply until Usagi snaps them out of their hypnosis.
As the Turtles, Usagi, and Kintaro rest after an eventful trip through a haunted forest, Jei used his dark magic to induce a horrifying dream upon each of them. In it, Jei kills Michelangelo, Raphael, and Donatello. As Leonardo weeps over his fallen brothers, Jei proclaims that he sees the evil in him, and he shall purge it. Despite a valiant effort from Leonardo, he is also defeated by Jei, who tells him that being a child, he poses no threat to Jei. As Jei is about to strike a finishing blow, Leonardo covers his face and is awakened by Raphael, learning that Jei was behind the dream. Jei is then seen in his shadowy dwelling watching over them through his water bowl, mocking them saying that they are puppets and pawns of the gods.
Dressed up as a friend, he appears, unmasking his camouflage. However, with the help from Sumo Kuma, revealed to be the head monk and leader of the Temple, but was brainwashed by Jei as well the tortoise talismans, he retakes control over the mutants, after revealing he only wanted to gauge their potential as servants but this causes Kintaro to unlock his powers and attack the turtles. Unfortunately, Jei manages to grab a hold of Kintaro, while revealing to Usagi that he wanted this to occur such as Kintaro learning compassion and humility to unlock his powers. He further reveals that he will use him as a vessel to further his immortal life. He begins the ritual and the turtles return to hold Usagi back. Before Jei can achieve his moment of success, the turtles are revealed to have been freed by Kintaro's last attack and deceived Jei and Leo runs Jei through with his katana, causing the angry Jei to realize the Turtles are no longer under his control and use Kintaro against them. This enrages Usagi to the point that he battles and manages to finally defeat Jei, pulling out Leo's katana that manages to imprison Jei's soul within it, leaving Jei's empty body to plummet to his death after being dropped into the abyss and his soul trapped in Leonardo’s sword. This ends his threat for good.
Jei is a samurai who believes that he was chosen by the gods as an emissary, to smite evil and execute sinners. However, in his delusions, Jei perceives nearly everyone to be a sinner and has the tendency of killing anyone who draws his attention. While he is capable of acting normally, once in the throes of his madness almost anyone within sight is marked for death. Because of his brutal rampages, most (including Usagi) do not consider him an emissary of the gods, but under demonic possession, or simply insane.
Whether or not he still has his mental faculties, Jei does possess some supernatural power.
- Dark Magic: Jei has a variety of supernatural abilities to conjure spells, and can perform feats such as being able to see his enemy's location just by looking into a bowl of water, and summon beings from other realms, such as the Ninja Turtles.
- Hypnotism: Jei can also hypnotize others to his bidding, but only by looking directly into his soulless eyes. Which is why he usually accomplishes this by pretending to be a desperate old man asking for help to get close enough to look into their eyes. He was able to forge his own army this way and even temporarily brainwashed the Turtles to do his bidding.
- Sōjutsu: Jei is a master of the art of the spear. He is able to wield his his black-bladed yari in order to land deadly strikes and face off again numerous opponents, such as the Ninja Turtles, with little to no struggle, as well as skilled warriors such as Miyamoto Usagi.
- Immortality: Jei claims to have lived for more than thousands of years by passing his soul onto a stronger vessel and continuously done so.
- Black-bladed yari
- Jei is based on the slasher horror film serial killer Jason Voorhees of the Friday the 13th film series. His full name of "Jei-san" is a pun on the name "Jason."