Oligarchy Idea, please give suggestions!!!

I'm trying to come up with a government and this is what I have so far. The government in my story is an oligarchy run by these people called the Particulars, and they choose 9 (three from each sector) fifteen year-old's every year to train until they are 17 to become particulars but the thing is, only three of those nine (one from each sector) ever become particulars (the others vanish).The particulars are trained in a special sort of magic that is essentially enhancing the brain's power in order to bend the laws of physics. But the thing with the particulars is even though they govern the society, the people they govern don't know much about them, all they know is that if you go against their wishes, you will disappear, forever. The place they govern is divided into three sectors, Opus (bussiness), Theatrum (entertainment), and Sementis (agriculture).

Does anyone have any suggestions? I don't know what else to add that would give it depth.

I know that this probably isn't the type of advice that you were looking for, but what if instead of the other potential leaders disappearing you make the ones that "flunk out" become heads of law enforcement. The whole concept here is interesting.

if its based on a logical proposition then you give it am authenticity that makes it believable that it could be established by people like the reader.
Then like all human creations, it can be eroded and corrupted by the basics of human nature.
Why would a reader from a world where at least the marketing promises some form of democracy believe that an oligarchial world would be something they could be invested in?
What brought on the the paradigm they are ruled by?
You don't have to look far in reality to see some justification or even reflection.

In 1922 Dewey and Lippman argued over the fate of democracy and the conclusion they came to was that its was doomed because the average voter relied on hearsay, friends opinions, stereotypes or basic understanding of the issues to make a qualitive decision. Almost 100 years later and we have technology that we can use to talk to anyone in the world almost instaneously and access a worldwide of information and yet we still seem to beset by the same problems.
Some say the 'governed' are the problem and that a special board of experts could make the decisions, well, at least that was lippmans conclusion.

In the country that markets itself as the land of the freedom and democracy, it is classed already by some economists as an oligarchy and routinely destroys their branded ideals when its elsewhere for profit of a few. The journey into human folly has been repeated so many times in history, not many ideas are truly new.

Even in your own mind you should understand the journey to where you are today
What are the leaps of logic to get them there. If you make them simple, human and understandable, with real world examples for guidance, it may help you believe the world your in. You can sell things easier if you passionately believe in them.

Do you have the 'physics' of the magic system youre suggesting? How are the particulars suited to the position? Is it genetics, training, a special 'something'?
Maybe the disapearance of the other applicants could be the consequences of failing at the trials? The rest are rumours because of the secrecy
Does this mindbending physics power come at the cost of your sanity?
Do you have to become a heartless organic machine to cope with the role of governance of the many?
Is it a hive mind link between the final chosen particulars to work in a coordinated way so the story can be about relationships, compatibility and conflict?
What is at stake for the system to remain? What good does it do for the society to justify its existence?
Are the mind powers needed for existential threats? Is this just a boogeyman to justify it or are they fighting against the darkness?
Is the system inherently swayed against the suggested outcome? Is it a self fulfilling prophecy?
Does the sacrifice of rights for power give them the security thats worth the cost?

Thats my 5cents worth.
Actually its worth less than that. Covid-19 killed my job a month ago.
This is brought to you by boredom, the internet and nithing better to do ;P