Becoming a demon god is pretty straightforward. The most important thing for that to happen is Authority. A demon king accumulates Authority to become stronger and become a demon god. The major reason why Authorities are important to becoming a demon god is so that they will be able to manipulate their mark of sin itself and fuse with it so that they become a sin themselves. After all, a demon god is the personification of a sin. The embodiment of that sin itself.
Every demon gets a mark of sin when they become a low-rank demon. This mark of sin determines when they can evolve and what abilities they get when they evolve. The mark of sin is the root of the power system of demons. It is the foundation of demons and why they use sin energy instead of mana to elevate their state of existence.
The origin of the mark of sin is the abyss. The will of the abyss creates it and marks the soul of every demon with it. Contained within the mark of sin is a wealth of power. It is the source of all sin abilities pertaining to a particular sin. It is like a spring of power more powerful than the energy well of an abyssal plane. To gain control of the mark of sin is to gain absolute power over that sin.
To become a demon god, one must gain control of the mark of sin, understand it, tweak it to increase compatibility with the soul, and finally fuse with it. It is a very difficult process. Even the first step of gaining control is not easy. Something as powerful as the mark of sin that can grant power up to the level of a demon king cannot be controlled easily.
The mark of sin will resist change. The resistance will die down once a demon king gains acquire a higher Authority than the one that is in the mark of sin. That is why demon kings need a powerful Authority just to get started on it and to unearth its secrets.
Apart from the daunting difficulty of acquiring a lot of Authority, the deadline is also a time crunch. The breakthrough to becoming a demon god is a race. The first demon that fuses with the mark of sin gains absolute control of it. That means the mark of sin cannot grant Authority without the demon god's permission which prevents the creation of any more demon kings with that mark of sin.
The abyss is the one that usually grants Authority after the trial of the abyss, but the trial will become inaccessible without the permission of the demon god. A demon god can also remotely strip other demon kings of the same sin of their Authority. All Authorities fall under the control of the demon god and to fail to reach it first is to give up your power to someone else.
Aeternus is unique in his path. He doubts he has a competitor. The fact that he went through the trial of the abyss without the permission of anyone proves that there is no demon god in his path. But that doesn't mean he can relax. There's no reason not to believe someone is out there with the same mark. Even the smallest chance of it is dangerous. If there's a competitor, that competitor will be far from normal too just like he is. Such a demon cannot be underestimated. So he can't waste any time.
He walked out of the fortress that is being built around the growing altar. Then he stood in front of the fortress and began to experiment with his mark of sin while he wait.
He doesn't have a powerful Authority. His Authority is just Level 1 and will need 3 Celestials to reach the next level but he isn't powerless against his mark of sin. He could already modify his sin ability a little bit as a high-rank demon. He should be able to do more now that he has full control of his chaos energy.
The limited manipulation of his mark of sin that he has is because of the warping by chaos energy. He should be a demon of envy with a mark of envy but he has a mark of chaotic envy. Chaos might be difficult to control but it is acceptable to change. Chaos is basically constant change. So the difficulty of overcoming the resistance of his mark of sin to change is much lower.
There are disadvantages to his situation too. Understanding and changing his mark of sin might be easier but fusing with it will be more difficult than normal because he will have to fuse with Chaos. That fight that he started with Chaos energy in the womb of the demon sire has not ended. He has only gotten time to adapt and relax before their final confrontation. At the end of the day, the two of them have to combine and he won't have the help of the shield he created to protect his soul.
Days went by and the liberation army finally arrived.
Their presence was announced by the sound of drums and feet matching on the ground in sync with the beat of the drums. They came in an imposing manner as soldiers ought to do but they are extra imposing because of their height.
It is wise to take towering giants seriously especially when they wear matching uniforms and have identical grim looks on their faces. The look on their face is as if they have been asked to die which they in fact have been asked to do. They look ready and willing to die.
These towering giants matched in formation and created a steady noise of feet slamming into the earth in synch. The smallest one of them is 70 meters tall and the tallest is 110 meters. They are already all taller than Aeternus. Then there is the Colossi who followed behind the army. They have heights above a kilometer. All in all, they are an impressive sight.