Shinigami create the main story drive in Light Yagami’s adventures in the popular anime Death Note. While the vast majority of rules are mentioned throughout the anime, the many unique aspects and specifics of the rules can be difficult to keep up with. Functionally, they can be broken down into four categories: how to use the Death Note, how ownership of the Death Note works, how Shinigami eyes work, and the rules that govern the Shinigami themselves. This final category is the most difficult to understand simply because the Shinigami themselves are hesitant to reveal too much of their own nature to the individuals with whom they interact.
In Death Note, Light Yagami, a young genius, comes across a strange notebook that allows him to kill any individual whose name he knows. He uses this power to rid the world of all he deems evil in an effort to create his perfect world and fashion himself as a living god. The notebook belongs to Shinigami, which can be understood as either a god of death or as a grim reaper depending upon the translation. He acquires allies who also deal with Shinigami, and faces intelligent enemies who seek to stop his mad quest.
Relationship with the Owner of a Death Note
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The Shinigami haunt the owner of their Death Note, in doing so they must become visible to that human within 39 days of the first use. Interestingly, Shinigami have no obligation to explain how the Note works, though they often do. They also have nothing to do with the deaths caused by the Note. Therefore, if the Shinigami were somehow to die the Note would not lose its power.
The Shinigami, although they are able to see the names and lifespans of humans, are not allowed to tell the owner of the Note. They are also not allowed to be in the human world for a time period greater than 82 hours unless their Note is possessed by a human. There is also a curious respect for human life among these grim reapers, as they cannot hand their Note to a child under the age of 6, and they cannot kill an owner of the note unless they are the ones who handed that human the Note in the first place. Shinigami cannot reveal the owners of other Notes, and they can only reclaim their own Notes by killing the human who possesses it.
Shinigami can only return to their realm once the original owner of their Note has died and their name is written within the Note, or if they need to find the owner of the Note using observation holes.
Using the Death Note
While humans can only shorten life with the Death Note, by writing human names in the Note, a Shinigami actually extends his or her own life with whatever stolen lifespan that human had. Shinigami must also always keep one Death Note to themselves. This means that when they lend one to a human, it is a second Note that they somehow acquired.
Another method by which humans and Shinigami differ is in using the Note for revenge. Any Shinigami who uses the Note to avenge or save the life of an individual they favor will die, however, a human can do so without peril. Also, interestingly, while Shinigami must always maintain at least one Note, they aren’t personal and can be swapped between Shinigami with ease as has been seen in the show with Light’s master plans.
Shinigami Life
While Shinigami can die, it is incredibly difficult to kill them as they are immune to human physical attacks. The easiest way for a Shinigami to be killed is through punishment in the Shinigami realm. Punishment can happen on nine different levels, from level Extreme to level eight. Anything from level three or lower is fatal to the Shinigami. If a Shinigami kills a human without using a Death Note they are automatically punished in the Extreme level.
Shinigami also do not require sleep and view it as pure laziness. Similarly, while Shinigami can be either male or female they cannot copulate either with humans or other Shinigami. And finally, any Shinigami who knows the name and lifespan of a human, by having seen their face, can find that human using an observation hole in the Shinigami realm.
Throughout Death Note, Light uses what rules that he knows of the Shinigami in his favor, and occasionally against the Shinigami themselves. At one point cornering one of the Shinigami into killing herself to save his main romantic interest. Seeing Light manipulate the rules as he does makes it logical that the Shinigami are so reluctant to reveal the inner workings of their society. Furthermore, it makes sense that when they do so they attempt to make it as complicated as possible to prevent their own demise and disadvantage.