If a demon lord is lucky enough to pass the trial of the abyss then they will have to make a very important decision about their future. There are three crowns that they must select from. There is the crown of the king of the abyss, the king of demons, and finally the king of kings. Each one is heavier than the last. Their soul can shatter if the burden of the crown is too much to bear.
They may be weak and tired after being subjected to mental torture but they must pick one. The decision is really between the first two kinds of crowns The third crown is too troublesome. The burden of the third crown will continue to increase as you add more crowns to it and you will be hunted for bearing it. It may be a crown that keeps giving but it will also continue to ask for payment from you.
Now that the three options have been narrowed to two reasonable ones, the decision of which crown to bear has been somewhat made easier. Mind you that the decision has not become easy. It has become easier, and less difficult. So it is still difficult. They can't rest and make the decision when they are not literally in limbo with one foot in life and the other in death. They must answer now. What crown will they bear?
The choice is easy and simple for Aeternus. He selected the crown of the king of kings. The other crowns disappeared as soon as he made the decision. He can't change his mind now. The crown of the king of kings flew towards him and settled on him. Then it began to sink into his soul.
The presence of a foreign and powerful object in one's soul is not a pleasant feeling. The pressure alone as your soul is forcefully expanded to accommodate the crown is enough to shatter weak souls. It felt like his mind is being forced to expand by the infusion of deadly and volatile energy. He also knows that the volatile energy will explode at the first occurrence of imbalance and turn his soul into a grenade.
The crown sank into his soul and fused with his mark of sin. It completed the fusion process since his soul didn't resist it or slack from supporting it. Then the sensation of danger he felt from the crown disappeared. It has finally become his.
The crown appeared around his soul, like a golden ring snuggling a ball within it and protecting it. Then the crown pulled on his connection to the world above in a bid to continue his transformation on his body. If he doesn't have any connection to the world above, he will remain here and die. Since he has a strong connection, his soul was pulled out of limbo to the real world.
(YOU HAVE PASSED THE TRIAL OF THE ABYSS)
(YOU HAVE GAINED THE CROWN OF THE KING OF KINGS)
(CHAOS ENERGY HAS UPGRADED TO THE DIVINE RANK)
(YOUR EVOLUTION TO DEMON NOBLE IS STARTING NOW)
(ERROR! SENSING THAT UNIFIED ENERGY IS AT EXTREME RANK)
(REQUIREMENT FOR EVOLUTION TO DEMON LORD MET)
(YOUR EVOLUTION TO DEMON LORD IS STARTING NOW)
(ERROR! SENSING THAT UNIFIED ENERGY IS BEYOND EXTREME RANK)
(REQUIREMENT FOR UNIQUE EVOLUTION TO DIVINE DEMON MET)
(YOUR EVOLUTION TO DIVINE DEMON IS STARTING NOW)
(ERROR! SENSING THAT THE TRIAL OF ABYSS HAS BEEN PASSED AND A CROWN HAS BEEN ACQUIRED)
(REQUIREMENT FOR UNIQUE EVOLUTION TO DIVINE DEMON KING PARTLY MET)
(UNIQUE EVOLUTION TO DIVINE DEMON KING ABORTED BECAUSE OF LACK OF HALF-DIVINE STATS)
(REMEDY! DIVINITY FOUND WITHIN EXISTENCE)
(DO YOU WANT TO CONSUME DIVINITY TO MEET THE REQUIREMENTS FOR EVOLUTION TO DIVINE DEMON KING)
A lot of notifications bombarded him as soon as he cleared the trial of the abyss. His existence is an anomaly and the system that streamlines the evolution of demons had to take its time to figure out what is going on with him. He is a high-rank demon and should evolve to become a demon noble. That's how it should be. But what is required to become a demon noble is a unified energy at the pinnacle rank. He has more than that, hence the initial confusion.
If he already has extreme rank energy, then evolving into a demon noble will get him nothing. It will be a redundant evolution, so the system tried to find the evolution that is suitable for him. It was then that the system realized that he doesn't just have energy at the extreme rank, he has more.
The demon noble rank is the last rank that a demon can reach on its own. Demon nobles need the energy pillar of an abyssal plane to acquire the next rank of energy and evolve. Killing other demon nobles won't help towards meeting the requirement for energy. Then a demon Lord needs a lot of divinity from gods to reach the half-divine rank. It is then that they take the trial of the abyss.
It just so happens that his Chaos energy was clamoring for an upgrade before his evolution. And he underwent the trial of the abyss so that his potential will not be limited. So now he has a unified energy that skipped the pinnacle, extreme, half-divine ranks to become the divine rank. The system determined that a high-rank demon with such powerful unified energy must have a special evolution.
It is understandable that he will skip the demon noble rank. He already has Accumulation and a noble house. It is also understandable that he will skip the demon lord rank. He already has infinite energy and the Oath of the lord. Then normal demon lords go on to have half-divine unified energy from the extreme energy.
That means he has somehow managed to upgrade his Unified energy to the half-divine rank as a high-rank demon which is against all rules. So he was granted the right to evolve as a unique type of demon called the divine demon.