In the future some form of transhumanism will exist. Hopefully it will always be optional…
The more you have, the less you are
Upon reaching adulthood, for free from the government, anyone can have surgery which sets them on a trans-human journey that they control (or it controls them?)
All the necessary hardware and wetware is inserted, but most of it will remain inert until a crystal is inserted in one of the 7 receptacles, all positioned according to the chakras – the actual position is just to be cool, they are just switches.
You begin with the root chakra, at the base of the spine, which happens to be the least likely place that anyone will ever see where it is. There is no known device that can detect a crystal.
The crystals are manufactured by the government in a highly secure plant. All the crystals are the same, but can only be added to a person in the correct sequence.
If you make certain high achievements, the government will reward you with a crystal. Very few people will ever be successful enough to get all seven. At the start of the story, nobody has.
The 6th crystal is hard to hide, as it is inserted into the 3rd eye spot between the eyebrows. All trans-humans have a visible slot in the position.
Crystals are interchangeable, so if you managed to get one from someone else, by any means, you could add it to yourself. Removing a crystal however results in death.
So, wearing something that hides your forehead could be seen by bad types as an indication that you do have a crystal there, and five others besides. Dangerous.
The seven steps basically divide the journey from purely human to purely machine, in terms of soul, ethics and so on. The machine side of you is very persuasive and wants to become more machine.
The powers you gain can be [insert here]. We could make them a mystery, that the government doesn’t share, and transhumanists do not share. The public learns from observation and guesswork. Networks of detectives spring up.
Some remnant of the soul will remain in a 7-crystal person, but what gets that soul to the point means they are the right kind of soldier/enforcer/leader the government wants, a new uber-race.
Our hero (of course) is seduced by the potential for power, but comes to realise how wrong the program is.
The themes are obvious – government control, ultimate power, good versus evil, the dangers of technology. Possibly the transhumans cannot breed, so that is a topic these days.
The scope is wide-ranging. People tracking down and killing each other for crystals. Others working diligently to earn them, or buy one (as any billionaire can). Underground resistance movements. Battles with seven-crystal beings.