Becoming a transcendent is not so simple. If it were that easy, it wouldn't claim the lives of the unprepared who attempt it. Becoming a vitality core stage refiner and a mana entity can either be successful or failed. You can't die in the attempt. Things are not so for becoming a transcendent.
There are a lot of factors that determine the success of the endeavor. The first and most important is the control of the mind. There is a need for perfect control of the divine sense. It easy to control the free ownerless mana in the environment than it is to hold on to the mana tightly bound to the body. But if you can control your mind, then you will be able to control your body.
The second factor is resilience. The soul might be flexible but having it pulled is a very painful process. The soul will not only be pulled but it will also be pulled out of its comfort zone and out into the physical world. The soul sphere is the protection for the soul. It is obvious that bringing the soul out of safety is a bad idea.
You will feel existence crisis and pain as the soul is brought into the physical world. It will feel like you're dying and your entire being will try to resist it. You have to maintain control of the mind through the pain because what is an even worse idea than pulling the soul out of safety is letting go of the soul during the pulling process. The soul will tear if it isn't let go all at once and uniformly or it will break if it is let go far into the process of pulling it out.
The third most important factor is compatibility between the body and the soul. A soul will automatically take on a form the stronger it becomes. This form is based on the familiarity of the mind with the body. The soul will stop being a sphere and turn into the image of the person.
The familiarity between the soul and body can be increased with control of the body. The better the mind can control the body, the more familiar the body and soul become. Certain weapon systems like the momentum-controlling system of the battle sage monkeys provide familiarity.
Familiarity is very important if you want the body and soul to fuse. You would expect the soul of a person to be very compatible with their body but it isn't so. The soul is fundamentally different from the body. One is physical and the other is spiritual.
In a normal setting, they shouldn't cross paths at all. Becoming a transcendent is not normal. The soul and the body have been forced into contact but that doesn't mean that they will fuse because you want them to. A horse can be forced to water but it cannot be forced to drink.
If compatibility is too low, the soul will refuse to bind with the body which will prolong the process of fusion. If the person breaking through cannot bear the pain anymore then they will abort the breakthrough which is almost certain to lead to death as the soul is released. The soul will rush back to take its previous form then it will collapse under the strain.
So it is best to completely reform the soul in the image of the body before the breakthrough. That way, there won't be resistance more than usual.
The fourth most important factor is the mana conversion rate of the body and the strength of the soul. The higher the mana conversion rate of the body the stronger the hold on the body by the domain. And the stronger the soul, the higher the chances of it withstanding the stress of breakthrough and surviving the exposure to the physical world.
The fourth requirement, mana conversion rate, is the easiest requirement to fulfill. You just have to pump your body full of mana to the extent that most of your tissues are composed of mana instead of vitality.
Tolerance to near-death pain, control of the body, and control of the mind are much more difficult to achieve of which tolerance to near-death pain is the most difficult. Anyone can do their best in calm situations. But becoming a transcendent needs you to be able to control your mind and body simultaneously whilst under near-death pain.
All these requirements have to be met before someone can safely go through a breakthrough. Even then, they have to take it carefully and solemnly. Any error can lead to death. The only ones that don't worry are those with royal bloodlines. The law fragments inside their bloodline will mold their body and soul into the image of their ancestor.
Those with bloodlines will know when they are ready to break through. Their Instincts will inform them when they have met all their requirements. They can sleep all their lives and their bloodline will meet their requirements for them as long as they have access to mana.
They don't need control because the process will go seamlessly as if they have done it over and over again. Their body and soul will have the highest compatibility and won't resist at all, so they won't feel any pain whatsoever. That's why becoming transcendent is not a problem for descendants with royal bloodlines.
Helios doesn't have a royal bloodline so the process of breakthrough isn't automatic for him. He has to take it step by step but he has nothing to worry about apart from the Stigmata on his back. His soul has been reformed into the shape of his body right from his conception.
The figure of his soul is the form of a golden giant within his soul sphere. It is also complete with an imitation of the golden runes on his body. He made the runes and he is the most familiar with them so even his soul bears them. It is very important that his soul is familiar with the runes because they will be fusing with body and soul during the breakthrough.