Corpus of the Abyss

Corpus of the Abyss (深淵なる軀) is an undead organization that has been founded in the New World four hundred years ago.

Background
It was a group entirely made up of undead magic casters. Originally, this group had been formed to work for their mutual benefit and avoid conflicts. The reason for that was because the undead are treated as beings with unlimited lifespans, have the capacity to study magic together, and friction tended to develop.

Without these three great drives, undead invariably developed other, powerful desires, and in the case of undead magic casters, they generally tended to thirst for knowledge. For that reason, once a conflict over knowledge began, it would tend to escalate. Neither party would stop until it became a battle of extermination which would end with one side being annihilated. If the three great drives of the living were concentrated into a single point, they surely see that single desire would become uncontrollable. It was very common for the undead to be destroyed in this way, to the point where the living could destroy both opposing undead beings while they were absorbed in their feud.

Knowing this, the undead eventually came to recognize that it was wiser to make trades and to cooperate with each other within reason, rather than fight to mutual extinction over knowledge and magic items. In the end, a list of names was made within Granisle Inscription to bind them together under an oath. Everyone had a rough idea of who was studying what within the group. They shared their information to avoid feuding over resources due to duplicating each others’ efforts. However, there was no guarantee that each person was telling the truth about the contents of their research. For example, Kunivela himself was conducting secret research of his own.

Nevertheless, the research of the undead, for the members of "Corpus of the Abyss," their fundamental aim was to achieve great magical might.

The Vampire Princess of the Lost Country Arc
When Kunivela was considering the option of running away from Suzuki Satoru and Keno Fasris Invern, Corpus of the Abyss would have mocked the Night Lich's decision if they heard that he had abandoned everything and immediately chosen to flee. However, according to him, he would only have drawn that sort of reaction a year ago. Right now, the organization’s members would unanimously back Kunivela's choice and vouched for the rightness of his decision.

For a year, it was noted that some unknown entity was slowly, gradually hunting down the organization’s members. Because of that, the numbers in the group continued to dwindle over the course of passing time. Although they had many absentees in their meetings that were spaced years apart, they all met on a monthly basis. However, as more of their group members fell, they have recently decided to instead meet once every two days. Seeing everyone present at those meetings reassured them, but if someone was missing, the undead would worry that they would be next, and thus they would live each day in fear. Some of them had even started staying together.

Currently, of its 55 members, 21 of them were completely uncontactable. This was not just limited to members of the outer circle, but even founding members of the inner circle. Ever since the death of Granz Locker, roughly, at least 40% of the group’s membership had been destroyed.

In the end, the new conclusion was an unconditional surrender followed by begging for their lives. While some people had suggested fighting at first, they had all lost the will to go on and fight at this point in time. According to Kunivela, Suzuki Satoru was the person responsible for the killing of many members from Corpus of the Abyss. Not only was Kunivela slain by Suzuki, but presumably Granz Locke as well after the two were interrogated under similar ways and circumstances.

At some point, Suzuki kept several undead members of “Corpus of the Abyss” alive for the time being after using his [Undead Domination] skill to take control of them. During Suzuki's deathmatch with Cure Elim Los Malvar, he forced the undead into entering the battle alongside him, assisting their master against it. Some of these powerful undead perished from Elder Coffin Dragon Lord's most powerful Wild Magic spell, [Soulbreaker Breath].

The Hal Elf God-kin Arc
In the main timeline, Corpus of the Abyss persisted for another two hundred years and was still largely unknown to most of the world. But some time ago, Corpus of the Abyss fell under the control of a certain entity who found about organization through one of the outer circle members. That One then proceeded to display its strength to the membership. The inner circle of Corpus of the Abyss knelt before the entity, not to expand their membership but thinking its inclusion would serve as a deterrent against the strongest beings in the world.

Over time, the reign of That One proved to have no benefits to the organization. That One was found to be a coward and the worst leader in the assessment by members of the inner circle. Though it deplored the tier magic the organization used as filthy, it only ruled Corpus of the Abyss to selfishly take the research cultivated by the undead to strengthen itself. Eventually this led to some members of the organization to become dissatisfied Andes form a rebellion with the aim to oust what they deemed to be a parasite to their organization.

Strength
It is comprised of a group of undead beings who are skilled in spellcasting. Among those are beings who specialized in necromancy and belonging to a race of Elder Liches and Night Liches like Kunivela. Initially in its foundation, there were originally four Night Liches and three Elder Liches within the undead organization.

Two hundred years later, it became a complete organization. Thanks to an increasing number of undead members that join Corpus of the Abyss over the course of time, the seven grew by 48, becoming a large organization with 55 members, with the original seven each being difficulty rating 150 undead creatures. After having a history of four hundred years, the inner circle of the group rose from 7 to 9.

Each one of the members within the group have the strength to destroy countries. As powerful undead magic casters, they could take down a nation by themselves individually. Hence, everyone was known to act arrogant because of their tremendous power, which was why they rarely worked with each other.

Corpus of the Abyss had never worked together as a group. However, they no longer had the luxury to do so. Every undead in the group shared their information, looked out for each other, and joined their forces.

Types of Members
There were two kinds of undead who belonged to this organization. One kind cultivated their influence among the living and used them to achieve their aims. Among those from the living, such undead are known to negotiate with typically people from the dark side of society. The other had nothing to do with the living, working quietly for their own aims in the world. Very few people thought like the former, so most of their members fell into the latter category. As a result, they did not cause many ripples in living society.

Known Members

 * That One
 * Banezeri Anchas: The Abyss
 * Granz Locker: The Saintess of White
 * Krunui Log Entesh Na: The Crimson-Eyed Duke
 * Kunivela
 * The Death Rider
 * The King of Decay
 * Wise Wolf
 * The Elder of the Hosts
 * The Eaten
 * The Revenant of Yellow

Trivia

 * While not named, a secret society consisting of only undead magic casters was mentioned early in the series.
 * Very few people in the New World knew about the existence of this organization.
 * Corpus of the Abyss became the type of group that existed only in rumors.
 * The members were more than a century old. They have never once experienced fear until for the first time, an unknown being killed off several of their members mysteriously.
 * The research notes Suzuki Satoru and Keno Fasris Invern had recovered from the members of "Corpus of the Abyss" were all along with the topics of enhancing their skills to dominate more powerful undead, learning how to cast spells of higher tiers, enhancing the attributes of the undead and so on.
 * Suzuki recalled a time when he once encountered weak magic warrior riding a Soul Eater among the members of Corpus of the Abyss.
 * After Suzuki's years of hunting down their organization, six members have already decided to leave the group and run away from it.