- This article talks about the Title and Race known as Demon Lords. You might be looking for Eight Star Demon Lords.
In fact, the Demon Lord Title is feared so much that some individuals with great strength and notoriety at times proclaim themselves as Demon Lords even if they are not, and without knowing about the requirements that come with it. And because they are feared existences, almost nobody dares to challenge their integrity.
According to the Voice of the World, the title Demon Lord always refers to True Demon Lords, meaning that such an existence is approved and acknowledged by the World's Systems itself. The only reason the term "True Demon Lord" even exists is for individuals to distinguish between the actual and the self-proclaimed ones.
It is extremely difficult to obtain. Even those who have lived for many eons are not guaranteed such status. Orc Disaster was in the process of becoming one but was stopped in the middle of his transformation. Thus, the Demon Lords watch each other, in the hope of preventing others from evolving above them.
To ascend one must first fulfill the requirements. Following the requirements, one will enter the Harvest Festival and a personal transformation. Once the transformation is complete a new True Demon Lord is born. True Demon Lords may receive an Ultimate Skill. The Awakening of a new True Demon Lord can be sensed from anywhere in the world, meaning everyone will know when a new True Demon Lord is born. Also, direct subordinates of the newly awakened Demon Lord, meaning those subordinates that have a soul link with it, will receive a gift that makes them stronger and more useful.
Demon Lord's Seed
To become a True Demon Lord one must first possess a "Demon Lord's Seed". The Demon Lord's Seed is something along the lines of skill but not really a skill. Its only purpose is to allow the user to evolve into a Demon Lord and nothing more. Individuals who have the Seed can sometimes be called a Demon Lord's Seed as well.
It is unspecified as to what criteria one needs to fulfill to obtain the Seed, but it can be conjectured that one needs to at least be of the Demon Lord Class to be able to have it, since, after evolution, the power of the being becomes so great that there's a chance the newly born Demon Lord becomes incredibly wicked and chaotic. Hence one must already be powerful in order to control it.
Other than that, there seems to many other unexplained rules here and there that also allows one to obtain it. One possibility could be that the individual must be capable of ruling others. Or maybe s/he must have an overall evil alignment and have some degree of notoriety. Or maybe s/he needs to already be ruling over beings that are considered to be of evil alignments, such as Monsters.
If one has the Seed, then the next task would be to collect a vast sum of souls. The amount of souls needed for a normal ascension appears to be 10,000, as Rimuru and an alternate Clayman both prove. The souls do not have to be directly collected by the one partaking in the ascension, but rather as long as the deaths are conducted by their intention the souls will be collected.
Although, if two opposing parties are involved in the same soul collection period, the party who has more direct access or contribution to it will receive the souls. Meaning, that since Rimuru was killing the army, he received it. Similarly, if Benimaru had done the killing, Rimuru would have still received it, since the killer has a more direct relation to Rimuru. Conversely, if Laplace or the like had done the killing, Clayman might have gotten it.
Rimuru is able to awaken qualified subordinates through his soul corridor, which was established through the special effects of Gluttonious King Beelzebuth's "Food Chain" ability. This method, however, requires ten times the number of souls Rimuru himself had to use, namely 100,000. He is also able to awaken other qualified demons by transmitting the energy of 100,000 souls to them, by briefly establishing a soul corridor with them.
It is possible that the increased amount of souls needed for Rimuru's subordinates are due to the fact that they may not possess a Demon King Seed, but merely possess an affinity towards becoming or forming a Demon King Seed.
The Harvest Festival occurs once all the requirements are met and the one to ascend agrees to begin the evolution. Once it is about to begin, the Voice of the World will announce it and it will start immediately.
Some will lose consciousness or enter a hibernation state, while others will be able to maintain their composure. Others will struggle to control their new powers.
During the Harvest Festival, the one ascending undergoes a transformation in which they can physically and racially evolve, and gain a tremendous amount of magical power, notably ten times as much as their previous EP. Additional abilities and Ultimate Skill can be obtained during the transformation. There is also the possibility of a significant change in personality.
Additionally, the subordinates of the one who ascends will also receive "gifts" of power or ability.
Again, with the help of Beelzebuth's Food Chain and Raphael's calculations, it is possible for people with a soul link with Rimuru to receive spontaneous upgrades as long as Raphael has enough information.
It has been noted by Rimuru and Guy that this is the final form of monsters under normal circumstances and no matter how many souls they gather there are no ways to evolve further, however, naturally, there are exceptions to this rule.
Rimuru's power increased dramatically after awakening his and Guy's servants as True Demon Lords due to his Food Chain's Soul Corridor. While it's unknown if Guy's subordinates would count, as he'd only need to briefly establish a Soul Corridor to evolve them, Rimuru maintains a permanent Soul Corridor link with his own subordinates, this means that his power increased in direct response to their evolution and put his power level in the same league as those of the True Dragons Veldora and Velgrynd. Furthermore, Rimuru was able to evolve into an Ultimate Slime by absorbing Veldora's energy body while leaving his core intact, transforming him into what can, in theory, be called the 5th True Dragon. Continuing even further, after Wisdom King Raphael evolved into Manas: Ciel, she upgraded everyone's abilities to their utmost peak for the time and Rimuru was finally recognized as a Great Demon Lord by the Voice of the World.
Self Proclaimed Demon Lords & Demon Lord Class
Self-proclaimed Demon Lords are simply that, self-proclaimed. They have an EP of an A+ Rank monster (200,000+) and have close affiliations if not part of the organization of Demon Lords. Karion, Frey, and Clayman are such examples. Some individuals can even be called a Demon Lord even if they're not part of the officially recognized organization. A brief example would be Rimuru, who, while massacring the Farmas Kingdom army, was thought to be a Demon Lord even if he wasn't one (yet). Such individuals are 'capable' of becoming True Demon Lords but are not ones necessarily.
According to Mizari a normal Demon Lord Class being is between 200,000~400,000 EP (WN: Chapter 211), meaning that only beings that are equivalent in power to the Demon Nobles are allowed to have the audacity to call themselves Demon Lords. Since Demon Lords are generally prideful existences, they do not allow anyone below such strength to call themselves as such as it will ruin the image of Demon Lords, although, after Rimuru's ascension and the creation of the Eight Star Demon Lords, such actions were no longer necessary since all of the Octagram, except for Ramiris were beings equal to and beyond the S Rank. As such, individuals brazenly proclaiming themselves as Demon Lords even if they are not are likely to be crushed by the existing Demon Lords unless at least two approve of it.
Self-proclaimed Demon Lords have risen and fallen all over history and as such the Eastern Empire thinks that a demon lord is not truly a big deal. Indeed, even a powerful Knights Templar can defeat such Individuals with the use of Legend Grade Equipment. However the True Demon Lords are a completely different beast, rarely seen and legitimately powerful.
Known True Demon Lords
Even among the current Ten Great Demon Lords, non other than 4 people had become True Demon Lords.
–Fuse-sensei, Chapter 70 (WN)