"After all, the Storyteller died.... and that woman too. I would like to think that my worthless history--- came to and end."
Jun Kanzaki (神崎 潤 Kanzaki Jun), known as "J", was third in command of Simon Kamishima's cult. He is Simon Kamishima's tenth child and Kaname Kujo's second son, making him grandson of the Minister of Justice, Masamune Kujo, and half-brother to Otoya Kujo and K. While he is an enemy in the first season of the manga, he one of the anti-heroes in the third.
Jun has pale silver hair, light blue eyes, and is babyfaced.
Jun is clever and secretive, but also cheerful and friendly. He hides his feelings behind a smile, and has a tendency to pretend that everything is fine. When he's unsettled he bites his nails. He also has a sweet tooth. He dislikes people who are blindly loyal, and people who would do anything for someone. He likes Michael because Michael joined the cult to get to use his skills as a hacker, instead of joining because of Jun's father, like everyone else had. When he's angered, his smiles has the ability to send bolts of fear into people just by looking. He parttook in "K"'s Bloody Monday as the strategist to regain his freedom.
Jun grew up within his father's cult, around fanatics and crime. He was given a pocket watch that used to belong to his mother, when he was a child. When he was 14 and his father was arrested, he killed the member of the cult that was his caretaker and burned down the house he had been living in, erasing any pictures and physical evidence that could lead to him, making it appear as if Jun Kanzaki had died. Since then, he has only been known as "J" and has taken position as the main strategist for the cult.
J makes the plans for Bloody Monday, and holds the fort while K plays a good student and his father is inprisoned. He gets a little team handed to him by K so that he can have some manpower; Jacob, Cain, Abel and Michael. They cover up the detonation of a neutron bomb in Russia with the deadly virus Bloody-X (an incident called "the Christmas Massacre" where an entire town is wiped out) and then move on to Tokyo, where Kamishima is imprisoned. He arranges to have mercenary Maya Orihara join the faculty of Fujimaru Takagi's group's school, and when Fujimaru decodes a file Maya failed to retrieve, J makes Fujimaru's father, Ryunosuke Takagi, a fugitive. After Jack Daemon kidnaps Haruka Takagi to threaten Fujimaru into hacking into a transformer substation.
After Maya was captured by the government's anti-terrorist organization Third-i, he had her freed through one of his Third-i moles, Sayuri Hosho, and Fujimaru kidnapped. Fujimaru was made to delete Third-i's Christmas Massacre file, under the supervision of Michael.
When Fujimaru wants to meet the leader of the cult, J, the current leader with his two superiors being otherwise detained, meeths him at neutral grounds; a cafe. When Third-i finds their location and has them surrounded, a few of J's subordinates fakes having been infected by Bloody-X to cause a distraction, and Jacob crashes into the cafe with a truck to allow J and the other cult members to escape.
When Maya fails to retreive all of the anti-viral for Bloody-X, J gives her one last chance, because he has figured out why K hired her in the first place. She is made to join the group that is sent to free Kamishima from the prison, while J takes control of Mashiro academy and hold Masamune Kujo and some of the students, Fujimaru included, hostage. The students and Masamune are infected with Bloody-X. In exchange for the anti-viral, J asks for Kamishima to be freed. They come to an agreement but because of Maya's blunder, most of the students are saved. Mako Anzai is still infected, however, and they still need the anti-viral that J has.
After the group leaving the prison split up to avoid pursuit, Maya kills Kamishima by wishes of both K and J. This was why she was originally hired.
While J hands over the anti-viral, he makes another deal with Fujimaru. In exchange for some information, Fujimaru will arrange it so J can fake his death (a second time). J didn't tell him to send Otoya to the location of his "death" however, but he uses it to his advantage by telling Otoya that they have the same mother. Otoya shoots him, which almost kills J, but he is saved by Michael.
J and Michael run away from Tokyo and goes far south. He later gives Fujimaru the information that leads Third-i to find out that the Russian case of Bloody-X was actually caused by the radiation from a neutron bomb. After Fujimaru finds out that Mako is K, Fujimaru also learns that K is intending to blow up all of Tokyo from Tokyo Tower. After Mako's death at the tower, J contacts Fujimaru once more to give him a clue how to stop the bomb.
At the end of it, J meets up with Jacob, Cain and Abel, and those three decide to follow J until they know what to do from then on.
Prior to the second season, J had seen Masamune together with a corrupt politician in another country, and with some reasearch done by him and Michael, he found out that Bloody Monday had been plotted by Masamune, who had become Prime Minister, and that Bloody Monday was still happening, and that Masamune went by the alias Storyteller. It is revealed in the third season that he had been working together with a specific, unnamed country to retrieve America's Pandora Box, but he turned against That Country when he realized they were working with Masamune. He also saves the life of Hibiki, to use her as leverage on Fujimaru. He was the one that sent Hibiki to Fujimaru's side.
Prior to the third season, J had Michael contact Fujimaru and a meeting between Fujimaru and J is arranged at the cafe where they first met. J tells Fujimaru that Hibiki is still alive. They vacate the cafe after Fujimaru starts yelling at J about J being a terrorist, and once outside J tells Fujimaru of his discoveries surrounding the Storyteller. J returns Hibiki to Fujimaru, as a proof of his sincerity. As a result to knowing the truth and having Hibiki by his side to confirm J's story, Fujimaru joins hands with J and his team.
- He is played by Hiroki Narimiya in the live action drama.
- In the live action adaption, Otoya and him change order of birth, making J the older brother and Otoya the younger.
- He is 16 years old in the first season, 18 in the second, and 19 in the last season.
- He is 166 cm tall, has blood group A, and is a Gemini. It is likely he recently had his 16th birthday at the start of the first season.
- He carries a pocket watch that used to belong to his mother with him. It was given to him when he was a child and he was told that his mother had abandoned him.
- He likes to eat convenience store food that are close to their expiration date. He likes to eat things whenever he feels like it and is often seen eating CalorieMate. He likes both salty and sweet things.
- Team J keeps a black pet cat.