Overview
Shinigami vary widely in appearance, and their bodies are built in ways that would seem impossible by human standards. Like humans, Shinigami also can die, of sorts by extending the life of a human they care about(by saving them from certain death): the purpose of a Shinigami is to end life, not give it, and hence saving a human is contrary to their nature. Shinigami who die in this manner are reduced to dust. Their Death Note is left behind, however if it is left behind in the human world, only humans who touch the notebook can see the shinigami.
The main thing all Shinigami have in common is the Death Note. This supernatural notebook allows them to end the lives of humans before their times, adding the human's remaining lifespans to their own (e.g. a man who would have lived sixty years, but is killed by a Shinigami at forty years of age would add twenty years to that Shinigami's lifespan). In this manner, a Shinigami can extend their lives indefinitely, and cannot be killed through "mortal means" (being shot, stabbed, etc.). To assist in this, their eyes allow them to see the names and remaining lifespans of humans by seeing the faces of their victims. For the Death Note to work, the Shinigami must be thinking of the person's face as they write it in. Any cause of death can be written down; if none is written, the human will simply die of a heart attack after 40 seconds, although it cannot kill someone under 780 days old, or over 124 years old, or with less than 12 minutes to live. A human using the Death Note will not receive the same benefits as a Shinigami; while humans can kill people, they cannot increase their lifespans by doing so. A Shinigami cannot hand a Death Note directly to a child under six or give the guidebook of Death Notes to humans.
According to Ryuk, life in the Shinigami realm is incredibly dull; Shinigami pass the time by gambling with years of their lives, and using the Death Note is considered workaholism, and they only do it once in a while to increase their lifespan so they do not slack off entirely.
They are intangible in the human world, unless they will it differently. Their notebook cannot be touched unless they will it.
All Shinigami must possess at least one Death Note, a necessity to extend their lives. Should they manage to come across a second, it can be loaned to a human. The Shinigami must accompany the human until they die, the Death Note is willingly given back or the book is destroyed; should the human give the notebook to another human, the same would apply to the new owner; when said human gives away the Death Note, any and all memories regarding the Death Note are erased. Shinigami can explain the purpose of the Death Note to the human, but this is done at their discretion. They can also offer Shinigami Eyes to the human at the cost of half the human's remaining lifespan; however, while a human with the Eyes can also see the name and lifespan of most humans, they cannot see the lifespan of any Death Note owner, themselves included. Likewise, Shinigami cannot see lifespans of other Shinigami. In addition, Shinigami are forbidden from telling the Death Note owner their remaining lifespan, both because it would cause confusion and because a human aware of their fate might react unpredictably (in a negative way). While in the human world, Shinigami are invisible and inaudible to everyone except the owner of their Death Note and anyone else who has touched it. Other unrelated Death Note users can only see their specific Shinigami. At the beginning of the series, it is stated that humans who have used the Death Note are unable to go to Heaven or Hell upon their death, instead they go to Mu ("Nothingness"). However, it is eventually revealed that there is no afterlife and everyone stops existing when they die. Shinigami may be male or female. Shinigami cannot and are not permitted to have sexual relations with humans; they cannot have sexual intercourse with each other, nor can they reproduce. In addition, humans cannot easily tell which Shinigami are male and which are female. Death Note 13: How to Read adds that Shinigami may have emotions "relating to the opposite ." For instance Ryuk feels shy and embarrassed when Misa Amane hugs him.
Though Shinigami possess senses of taste similar to those of humans, they do not require food or nutrients to live, and many choose not to. In addition Shinigami do not need to sleep and will not die from a lack of sleep; Shinigami view sleeping as "evidence of laziness."
Shinigami also seem to age, as seen in Death Note Relight: Vision of a God. Ryuk looks much older than he did in the regular anime.
The Shinigami have a language; each Shinigami has his or her own written language, with some opting for letters and some opting for pictures. Takeshi Obata, artist of the series, said that he assumes that all Shinigami can understand the languages of one another.
If a Shinigami breaks the laws that govern them, the Shinigami will face one of nine punishment levels. The severity is least at Level Eight and most at Level One; in addition an "Extreme Level" exists. The Shinigami will die if a level below Level Three is applied to him or her.
Shinigami may not kill a human in any manner outside of using a Death Note; killing a human without using a Death Note merits "Extreme Level" punishment.
Shinigami have rankings, with the King of Death as having the highest ranking. 13: How to Read states that the rankings do not "seem to affect" the Shinigami's "day-to-day activities" "very much."
Read more about this topic: Shinigami (Death Note)