Six Death Notes

"Only 6 Death Notes are allowed to exist at a time in the human world."

- How to Use: XLIX

"In the event that there are more than 6 Death Notes in the human world, only the first 6 Death Notes that have been delivered to humans will have effect."

- How to Use: LII

Six Death Notes are prominently used in the film Death Note: Light Up the NEW World and its novelization.

Overview
In the film and novelization, the Shinigami King says that whoever finds a new Kira can become king after him. According to the rules, only six Death Notes can be active in the Human World at once. So six shinigami bring six Death Notes to Earth, which are initially used by six different people.

Yuki Shien and the Japanese Task Force both try to collect all six Death Notes. If Shien collects all six, then the notebooks can only be used for Kira's purpose. If the Task Force collects all six, then the notebooks can be secured, preventing anyone else from using another a Death Note on Earth.

The six Death Notes' initial human owners and shinigami in the new series:
 * Alexey Ivanov, shinigami Sidoh
 * Sakura Aoi, shinigami Bepo
 * Hikari Yagami, shinigami Ryuk
 * Ryuzaki, shinigami Arma
 * Roger Irving, unnamed shinigami
 * Kenichi Mikuriya, shinigami Eve

Shien tracks down most of the Death Notes, which he passes to Mishima before his death. When Mishima is captured, all six Death Notes come into the possession of the Task Force.

The six notebooks are given to a group to contain. However, the unit transporting them to a secure location is attacked. Some of the Death Notes are destroyed, but at least one is in use again and people begin dying of heart attacks. Which of the six Death Notes were destroyed is not revealed.

Alexey Ivananov's Death Note
The Death Note first seen in the film is picked up by Alexey Ivanov. The shinigami who brought the Death Note to the Human World is Sidoh, although he is unseen in the film. Ivanov uses it to commit mercy killings on those who wish to end their lives.

Ivanov is later killed by Yuki Shien, who takes ownership. Shien later passes it to Mishima just before his death.

Sakura Aoi's Death Note
The second Death Note depicted in the film is owned by Sakura Aoi. This is also the second Death Note revealed in the prequel miniseries Death Note: New Generation. The shinigami who brought it to the Human World is Bepo. Sakura first uses it to kill Karin Kanatomo, and later to go on a killing spree.

Upon Sakura's death, ownership would presumably pass to Ryuzaki, although this is not elaborated on in the film as Bepo is not seen again.

Hikari Yagami's Death Note
The third Death Note revealed in the film is used by Yuki Shien to kill Sakura, but Shien is not the initial owner. This Death Note is also the first one seen in the prequel miniseries Death Note: New Generation, and it is the same one that was used by Light Yagami and Misa Amane in the first two films. L burned this Death Note after Light's death, and how it exists after that is unexplained.

Ryuk brings the Death Note back to the Human World to give to Light's son Hikari Yagami. Hikari uses it with his guardian Teru Mikami as a new Kira. Hikari's first shown victim is Rokuro Natsugawa.

Mikami eventually kills Hikari and takes ownership, but he is immediately gunned down by Tsukuru Mishima and ownership falls to him. Mishima later has Ryuk pass the Death Note to Yuki Shien, who uses it to help him track down the other Death Notes in use in the Human World. Shien later passes it to Misa Amane to gain her trust and cooperation. Upon Misa's death, ownership passes back to Shien, who passes it back to Mishima before Shien's death.

Ryuzaki's Death Note
Ryuzaki is shown to have one of the Death Notes, and the shinigami is Arma. How Ryuzaki obtained the Death Note, such as if he tracked it down through a case, is unclear.

Ryuzaki is the sole owner of this notebook.

Roger Irvinig's Death Note
Roger Irving owns one of the Death Notes. The shinigami attached to this Death Note is unnamed, and they are described in the novel as being large and quiet.

Irving is a wall street broker who uses his Death Note to kill select clients and make money. He is eventually tracked down and killed by Yuki Shien, who takes ownership. Shien passes the Death Note over to Tsukuru Mishima before his death.

Kenichi Mikuriya's Death Note
Kenichi Mikuriya owns one of the Death Notes, and his shinigami is named Eve. Mikuriya is a Supreme Court Justice who uses his notebook to kill Kira supporters.

Mikuriya is eventually tracked down and killed by Yuki Shien, who takes ownership. Shien passes the Death Note to Tsukuru Mishima before his death.

Trivia

 * While the Death Note originally picked up by Light Yagami in the first film returns, the Death Note given to Misa does not.
 * Another Death Note used in the film is Arma's Death Note, which she uses only once to kill Sho Nanase.