Demon Possession

Demon Possession (悪魔憑き) is a strange disease and magic curse cast by the demon king, Diablos, that affects people born with the demon Diablos' blood in their veins due to being the descendants of the Three Heroes that defeated him. It is a sudden event where a woman's body suddenly begins to rot until it is not recognizable as a human being anymore and dies one day.

However, it is reveal that this symptoms is an form of magical overload that manifest on the female desendant of the three hero, which leads to the afflicted suffering from physical degeneration as it progresses, thus leaving the afflicted to become a lump of flesh until they die.

Overview
Demon Possession is a state in which the excessive magical power that has been inherited by the female descendants of the Three Heroes of each tribe of Elves, Beastkins, and Humans who subjugated the demon Diablos, which manifests in the blood of the heroes' descendants to varying degrees depending on the lifespan of the race which is too powerful and has gone out of control.

At a certain stage depending upon the species' lifespan, the cells will begin to take over a female descendant's body and eventually transform them into a monster. The rate of occurrence decreases as the blood of the hero generation fades due to the change of generation, which is rate on the elves, follow the beastkins, and finally humans.

Humans who have undergone many generational changes have a higher occurrence rate of demonic possession, while Elves who have fewer generational changes, have a higher occurrence rate. The greatest percentage of those who manifest are elves, due to their long lifespan they are fewer generations removed from the time Diablos was slain.

This symptoms mostly afflicts on the female, while on the male case is very rare.

Background
After being killed by the legendary Three Heroes, Diablos placed a curse on them so that they and their descendants would suffer painful deaths. Without exception, the affected patients collapse into ugly masses of flesh, and are hated and abandoned by their families, also cast out by the society.

Due to the sufferers being a descendant of the Three Heroes, The Church then tell the public to hand over the symptoms of possession, even takes over for a fee and order these individuals to be executed under the guise of purification, in order to free them from suffering by stating that those who are possessed by demons are monsters that can infect others who are close to them. They claim that they are protecting the common folk, but not before as they actually trying to disposes of it and use them through human experiments for their research experiments.

Symptoms True Identity & Cult's Propaganda
Demon Possession's true title is the "Curse of Diablos" (ディアボロスの呪い), which only manifests and afflicts in females itself because the heroes who fought Diablos were females. Its true identity is that a person who was implanted with Diablos Cells in an experiment by the Cult of Diablos in the past was unable to adapt to the cells and had a rejection reaction, causing the cells to go out of control.

Diablos cells are controlled by magic, so if the person himself has enough magic power control ability, or if someone else controls it from the outside, it will adapt to the cells and the body will not collapse. The Three Heroes were also implanted in the same way and as a result of inheriting Diablos cells when they gave birth to their offspring, people with Diablos cells spread and the phenomenon of demonic possession began to be seen all over the world.

In order to hide the existence of the experiment, the Cult of Diablos, with its roots deep in the Church, change the true name into "Demon Possession" and treats it as a "disease" that should be avoided, and prioritizes hunting and executing those who have demon possession until disposes of it at the church to prevent the truth from being exposed. The world has been led to believe the Cult's propaganda, as the reality it's that the Three Heroes were each implanted with cells taken from Diablos by the Cult.

For this reason, it has become a business to bring demonic possessed patients to the church. The cause is that a large amount of magical power accumulated in the body went out of control. Therefore, it is possible that these patients have great power, and the Cult calls these individuals as a "Compatible" (適合者) and strives to secure them.

The reason why the Cult tried to find any individuals who which already had a possessed symptoms was because the occurrence rate had decreased with the change of generations, which made the amount of Diablos cells is much decrease considerably since they were becoming the main ingredients for to creating the Tears of Diablos.

Curing Demon Possession
While Demon Possession can be cured with magic, it is said that the Cult of Diablos had tried in the past but they couldn't create a cure, as the curse was very powerful comparable to a Demon king, assuming it wasn't there was a cure for it, which consider as a lost technique.

That is until Cid Kagenō in his young age manages to discovers one of these people undergoing the effects of Demon Possession and doing magic experiment by trains his ability to use magic through the individual's enormous amount of magic power seeping from it. In consequence, Cid gained an enormous amount of magic power and control. When Cid completely suppressed the magic deviation that was going out of control inside the possessed body, he accidentally managed to heal Alpha and established a cure to return it to its original form. A side effect is that the afflicted's magical power will increase a bit, after being healed of their curse, but only by 5-10% just once.

All of the Seven Shadows of Shadow Garden had Demon Possession until Cid cured them. Cid also curing his sister from demonic possession when she turned 14 years old, thinking it an error in her mana flow.

Before or after Seven Shadows leave their lord, Cid, Alpha and Epsilon are able to cure the people who had the Demon Possession beside Cid and they are able to recover any individual who have a possessed symptoms, also subsequently recruited them into the Shadow Garden organization when the "Seven Shadows" began their membership expansion. After that, it was used by Shadow Garden on manifesters, and they used the cure method to increase the number of members along with treatment. Most of the Shadow Garden members below Seven Shadows have experienced the disease, and the fact that they saved them from that situation is the source of their loyalty to the organization.

Eta's Theory Research Relation on the Vampire Progenitor's blood
Eta was conducting an research about the Demon Possession on the Vampire Progenitor's blood, to which she acquire a certain hypothesis theory. Over the course of her research, Eta discover that there’s a possibility that the blood of the possessed and the blood of the Progenitors share the same origin and that the two merely diverged as they were inherited from parent to child.

For certain result, Beta will go to the Crimson Tower at the Lawless City, where the Vampire Progenitors reside and take a blood sample from a Progenitor, so Eta could check for her lab progress. Also, her job is to continue surveying the materials in the library and collecting anything which is important to further the theory research.

After Beta already securing the Blood Queen’s blood and seals it in a vial, she take them to the lab where Eta would analyze it. By the time of the conclusion research progress, Eta’s theory was proved to be valid. With the Vampiric power that could be useful together with proper training, Shadow Garden are able to mastering the Progenitors technique.

Trivia

 * Cid Kagenō figured out that Demon Possession is symptoms that afflicts the individual with high mana are at risk of losing control of it, which becomes a mutation state.
 * It was then Cid are able to know how to reverse the transformation by experimenting on the mutated Alpha, which not only restored Alpha but also granted her control over her increased mana.
 * During the experiments, Cid also figured out how to replicate the effects in himself, increasing his own power in the process.
 * Every member of Shadow Garden is a girl who succumbed to the "curse", which was subsequently healed and all of them from the descendants of the Three Heroes have at least decent magical abilities.
 * During membership recruitment, Eta created a device known as Locator of Possess, that which could track anyone with possession symptoms who would later be cured and recruited by Shadow Garden.
 * Although Alpha and Epsilon are the only ones so far that can heal the Curse of Diablos, apart from their lord Cid, apparently only their lord, can heal all kinds of afflictions and curses thrown from their enemies, like when he heal everyone which afflicted the Vampire's curse during the battle that Cid/Shadow had against Elizabeth at the red tower in the Lawless City.