|Information important to every Death Note can be found on Death Note (object). A complete list of rules of how to use a Death Note can be found on Rules of the Death Note.|
Sidoh's Death Note is the first Death Note seen in the series, and the first notebook used and discovered by Light Yagami. This Death Note would ultimately change Light's life forever, turning him into the mass murderer Kira who targeted criminals.
The notebook has a black cover with the words DEATH NOTE written on the front. Inside are white ruled pages. Based on the side of the notebook that Ryuk wrote DEATH NOTE on, the notebook opens on the right side and apparently reads from left to right. The inside of the Death Note contains the basic rules of how to use it, which are written in English on the back of the notebooks front cover. These rules were added by Ryuk, and were not originally present inside the notebook when Sidoh owned it. Light later asks Ryuk to write two fake rules in the Death Note, which Ryuk adds to the inside back cover.
The five rules written by Ryuk are as follows:
- “The human whose name is written in this note shall die.”
- “This note will not take effect unless the writer has the subject's face in their mind when writing his/her name. Therefore, people sharing the same name will not be affected.”
- “If the cause of death is written within 40 seconds of writing the subject's name, it will happen. ”
- “If the cause of death is not specified, the subject will simply die of a heart attack.”
- “After writing the cause of death, the details of the death should be written in the next 6 minutes and 40 seconds (400 seconds).”
Light makes some small additions to the rules of the Death Note. He has Ryuk write them on the inside back cover of the notebook. Although the rules are fake and unable to take effect, their inclusion in the notebook allow Kira to stay one step ahead of L, then ultimately defeat him outright.
- “If the owner of the Death Note does not write a name in it for 13 days, consecutively, he or she will die.”
- “If the Death Note is burned or destroyed, all who have touched it will die.”
Sidoh's Death Note was stolen in the Shinigami Realm by Ryuk, who wrote the rules of how to use it inside the notebook, and dropped it into the Human World. The notebook was then found by Light Yagami in the courtyard of his high school in Kyoto, Japan. Later in the story, Light gives his notebook to Ryuk, who gives it to Rem, who was instructed by Light to later give it to a greedy human who would use it for his own gain.
As part of his plan to erase suspicion of him being Kira, Light turns himself in to the Task Force, and says that there's a possibility that he might be Kira unconsciously. While being monitored in a prison-like cell within Task Force headquarters, Light signals to Ryuk that he is giving up ownership of the Death Note and loses all of his memories. It was then given to Kyosuke Higuchi by Rem. Because Light is incarcerated while Kira killings begin to happen, L has no choice but to release him. Light begins working enthusiastically with L to find Kira, now unaware that he ever was Kira. After L falls into self-declared depression because his "evidence" no longer adds up to Light being Kira, Light begins trying whole-heartily to find Kira and eventually discovers a lead: the company called Yotsuba. After Misa proves the identity of the new Kira, Light and L arrange for the arrest of Higuchi. The two arrive at the scene of Higuchi's capture, and Light gets his hands on the Death Note, causing Light to regain his memories. Light holds on to the notebook in order to keep his memories (which would disappear if he let go), and he kills Higuchi using a piece of the Death Note he had hidden in his watch. With Higuchi being dead, Light becomes the Death Note's owner once again. The Death Note ends up in the hands of the Japanese Task Force, though Light is still its owner.
Soichiro Yagami later trades the Death Note to the Mafia, who kidnap Sayu Yagami and ask for the Death Note in exchange for her life. The Death Note was then given to Jack Neylon by Mello. (Although Mello holds the Death Note quite often and considers it his property, he never technically gains ownership.)
The Death Note is recovered from the Mafia and given to Sidoh by Light, who takes it back to the Shinigami Realm. However, Light has the remaining pieces from Sidoh's Death Note and uses them by hiding it in his watch upon releasing the activation until his defeat.