The Shinigami Society : canon, headcanons, and theories
We don't know a lot about the Reapers' lore in Black Butler, so I wanted to write about what we know, what we can analyse and what we can theorise.
Keep in mind that I am going to take all of the information we have about the reapers, including from the musicals, the official arts from Yana Toboso, the OVA "The Tale of Will the Shinigami" the webradio, the character songs, etc.
Also: English is not my first language, so sorry for the mistakes
What we know about the Reapers
We know from the manga that all Reapers are humans that unalived themselves. Their role is to review humans' memories (represented by what the manga calls "Cinematic Records"), not to send their soul into some kind of good or bad after-life, but to make sure that the human HAS to die, in case they were supposed to change humanity in a good way later in life. If the Reaper considers that the human is "worth saving", then the human can be saved. But it almost never happens. The Reaper has to be impartial in his analysis.
Demons are their natural ennemy, since they eat the souls they have to protect/collect. However, according to the Kuroshitsuji Web-Radio, fighting demons is not really part of their job. William says that if there had to be a video game about Reapers, it would be a work simulator game, with points whenever the player collects a soul. Fighting demons would be more like a bonus stage.
Reapers are of course able to defeat demons if needed. They are trained to fight, but being a good fighter is not mandatory (Othello, for example, cannot fight.) According to Grell, Reapers are naturaly stronger than demons (None of the Reapers are even afraid of demons, including Ronald who is quite unexperienced.)
Since Reapers are all ex-humans, they have feelings, and have to sleep and eat to function (unlike demons). They are however way stronger and resistant than humans, and have immortality. They are not invicible, though: they can be killed by a Death Scythe, or by the Thorns of Death, an illness that Reapers can get if they let the Cinematic Records of a human penetrate them and reach their heart.
Reapers all have greenish eyes and bad eyesight which forces them to wear glasses. They may have the ability to change small details in their appearence such as hair color, but it could also be something that only Grell can do. It's also possible that they all have sharp teeth, but that most of them choose to hide it.
They can choose to appear to humans or not. Humans that are familair with death such as O!Ciel are able to see them, even when they make themseves invisible.
The Shinigami Society and how the system works
Reapers are first trained at the academy, where they learn Ethics, Practical and Theory. To become full Reapers, they have to have at least a B average and pass a final exam that consists in reaping and evaluating a human that is about to pass away. According to William, the true meaning of a Reaper is to learn the value of a human life, but it may be his own personnal opinion.
Reapers can have different functions inside the society: they can go reap souls (Grell, Ronald...), supervise a team (William), work in the science department (Othello), teach at the academy, make the glasses (Lawrence Handersen) and there are also services like Human Ressources (that William hates) and even an Optic service to evaluate eyesight. Their bosses are simply called the "Higher Ups".
Reapers can volonteer to teach young recruits on their own worktime.
The Society has different departments everywhere in the world.
The Reapers all wear a black suit, and each of them carry a Death Scythe. However, they are allowed to custumize both the suit and the scythe, as long as it stays somewhat sober and practical. Some Reapers can negociate to have better custumized scythes if they know the right person within the company (that's what Ronald did to have a lawnmowner)
The Reapers are expected to follow the rules without asking questions. According to the musical and the manga, here are a few:
They must all wear glasses
They must take care of their Death Scythe
Sundry expenses are paid at the end of the month
They must not express their feelings while working
If they see someone handsome, they must consider this encounter as their remunaration (according to Grell, so probably not a real rule)
They have to have a party after work (according to Ronald, so again, probably not a real rule)
They must not kill someone that is not on the Death List
They also have to have discipline, to always be punctual, examplerary, and have a certain etiquette. But that doesn't keep them from all having different personnalities, some more inclined to fit the "cold worker" image than others.
Surprisingly, they don't have to hide their identity to humans, even when they are investigating on a case. Most of them do it because it seems to be the logical thing to do, but there is no rule about that. (William infamously never hides his identity for example while Grell disguised herself as Madam Red's butler.)
If a Reaper desobeys a rule, they can be demoted. They are given a weaker Death Scythe and have to do a desk job for a while. Physical punishment may also be a thing, but it could also just be the way William treats Grell.
They are allowed to have a "life" outside of working. Ronald goes partying basically every evening, and in the Webradio, he keeps saying how he likes to flirt with the girls with his male co-workers (implying that they are allowed to have romance at least with other Reapers.)
They can't quit, but they can desert by leaving/breaking their glasses, like Undertaker. They become outlawed in the eyes of the Society, but keep their Reaper abilities and Scythe.
Reapers earn a salary, but they often have to do unpaid overtime. It is implied that they are not paid well, despite the job being hard and demanding. The headquarters seem to be more modern than the 19th century England setting of the manga, and they also use modern tools. They use pigeons to communicate.
They seem to obey some patriarcal rules, since women are only seen working as secretaries or in the administration, never in the field or higher positions.
2- Theories and headcanons
Who are the Reapers working for ?
We know that Hell is a thing in the Black Butler Universe. If we take into account the non-canon part of the first season, Heaven also exisits. We can theorise that the Reapers are part of some kind of in-between, maybe Limbo.
Imporant detail: the Reapers are called "haken" in japanese, not "employees". "Haken" are workers that an agency sends to a company for a short-term contract. That implies that the Reapers are sent by someone, and are not actually part of the Society. The Society could be led by some entity that is NOT a Reaper, and the Reapers themselves could be sent to work there maybe by Death?
I don't think that Reapers hold a lot of power in the Society, even if they have an higher position than simple workers, like William.
Speaking of William, as a supervisor, he is the one that is trashing on the Society the most, which adds to my theory that the Society doesn't give a lot of credit to the Reapers. I think that the Society is shady as hell, and is hiding something that not even the Reapers know. That may be the reason Undertaker deserted.
The job of a Reaper is anyway pretty pointless as it is, since they are here only to make sure something that never happens (a human being saved) doesn't happen. So...why are the Reapers even here? What purpose to they serve?
Who do they collect souls for...?
Who killed the Phantomhives...?
That is my BIGGEST theory, but what if the reason we know so little about the Reapers is because it's the Society that ordered the death of the Phantomhives? Maybe Yana Toboso is keeping information from us to have a better plot twist?
I mean, it's kind of clear that Undertaker was very close to the Phantomhives. What if this proximity was seen as dangerous by the Society, and they decided to kill them?
It is never clearly stated that Reapers can be redeemed if they work hard enough. They are punished because they cheated Death (in a way) for unaliving themselves, but it is not said that they can eventually rest in peace.
I think that the Society WANTS the Reapers to think they can be redeeemed to make them work hard, but that it's actually not the case (or maybe very rarely). William implies it in his character song, when he says that he will basically drown himself under work and embrace his solitude forever. (Maybe he wanted to become a supervisor to have a better chance to be redeemed only to understand that...there is no redemption.)
There is definitly something with Reapers and eyes. It's the only trait they have that seperate them from looking like regular humans. I think that their eyes are made to see the invisible (Death, souls...) and therefore, are not good at seeing the living world. As if their eyes were the proof that they don't belong to the world of the living anymore. So, in order to see "the real world" correclty, they have to wear glasses. I also think the glasses, in a way, help them hide their emotions. I know for a fact that I feel way more vulnerable when I don't have my glasses on. They may be wearing them like a mask, to stay detached.
Glasses could also be a way to protect them from always having to see demons and other dark entities, like in JJK.
Why do Reapers have to stay cold?
As I said, Reapers are expected to be cold, detached, and to not feel anything. But I wonder if it's actually part of the rules, or if it's a non-official rule that the Reapers created themselves to protect themseves from the Thorns of Death.
As we saw in "The Tale of Will the Reaper", the Cinematic Records can penetrate a Reaper if they show some kind of vulnerability. Then, they force the Reaper to feel for the human they are reaping, until those memories reach their heart and kill them slowly. It would make sense that the "no feelings at work" rule comes from more experienced Reapers, as an advice for younger recruits, and not as an official rule from the Higher-ups.
I think that Reapers do age, but very slowly. There is at least a notion of aging within the Society, since all of the Reapers at the academy seem to be younger than the more experienced ones. Lawrence Handersen for example is seen as an older Reaper, and he definitely aged between the time William and Grell passed their exam, and the current time of the manga. Grell and William themselves seem somewhat older from their academy years. Ronald, a young recruit, also looks way younger than Grell and William, and even points out that Grell is "old". William also seems to have aged between his first appearence in the Jack the Ripper arc and the last time we saw him (he is seen having slight expression lines) but it could just be Yana Yoboso improving her style.
I think Reapers all start as older teenagers (even if they died older, they get back to looking somewhat 17). They then age very slowly. I theorise William and Grell to look in their early 30's in the current time of the manga (they seem "mature" enough to not be considered as young adults) so we can say that they age around 15 years each century (Their exam took place around 100 years before the events of the manga).
Just like humans, some look "older' than their age (William and Grell are the same age in Reapers years but William looks older, probably dued to stress). It could also be possible that a Reaper that died older will age faster.
The reason why they all start as older teenager and not as the age they were when they died is because it is easier for the Society to evaluate the level of experience of each Reaper like that. It would be harder to track if, for example, a new Reaper looked 67 while an older one looked 25.
This aging process could imply that they can eventually die from old age, at around 500 years old. That could also mean that they can retire, which checks up with what Alan and Eric say to Grell in the musical (something like "We can't wait for you to retire").
Reapers seem to use tools and suits from different time period. I personnaly think that the Shinigami realm is located out of time and space, in some kind of dimension where they have access to technologies from different times.
Reapers and gender identity
This headcanon is very specific because Grell exists. William and Ronald often complain about her, but they never make any kind of remark regarding her gender (or her preference for men). William is mostly annoyed by her lack of regard for the rules (and dress code), and he hates that she shows affection to Sebastian because he's a demon, not because he's a man. I personnaly think that Reapers are able to see souls. One of the thing they have to learn, is that the soul prevails the body, therefore what matters is that Grell's soul is that of a woman, regardless of her biological male body.
That's it for today, feel free to add your own theories!