Stigma

Stigma is a secret organization in the FanFiction High School DxD: True Maou written by demonicjester01. Its objectives consist of maintaining a nonviolent status between all of the mythological factions (therefore making them opponents to the Khaos Brigade), as well as slaying the abominations known as Apostles. Their ultimate goal is to slowly, but surely bring about a new world by "destroying" the current one.

Summary
The group functions as an independently acting cell in which individual members inform about or take care of problems that arise near their location. Said problems can range from high-ranking members of a certain faction risking conflict with another to an Apostle appearing, both cases in which the course of action would be immediate elimination of the target. All of the members of Stigma carry an indigo mark in either the left or right eye, while the Grandmaster carries it on both.

The organization maintains ties to many of the mythological factions through it's members, most of which hail from different backgrounds. They also have a strong underground presence in the human world, with many members taking jobs ranging from protection and entertainment to spying and assassination.

Stigma's members seldom meet together, and it is seen as a great risk for three or more to be in the same place at the same time. Despite this, they tend to work in pairs chosen by the Grandmaster on the basis of skill compatibility and balance, but not so much on personalities. Due to this, people like Aslatiel and Shimadal are paired together in spite of the former's dislike for the latter.

Grandmaster
Despite being the founder of Stigma and the man all members follow, little, if anything is known about the Grandmaster. With even his name being unknown to Stigma's members, he's one of the most mysterious entities to appear. He acts like a father to the people he has recruited, and appears to care for them to a certain extent, giving Aslatiel complete freedom of action to remain in Kuoh Town for the time. Even so, he commands absolute respect and obedience from most of his subordinates, which suggests great power and charisma. He bears the mark in both eyes.

Members
The main body of Stigma consists of ten members, most being of different races and specialties. Taking many aspects into account, they are ranked in accordance to their overall usefulness to the organization. In terms of combat potential, the weakest members of the group are still quite formidable due to their utility skills, while the stronger ones are capable of fighting equally with or even defeating enemies on par with a Satan-Class Devil.

No.1 Niphelia
The strongest member of Stigma. Being Number One exclusively due to her battle skills, Niphelia has unimaginable combat capabilities that allow her to fight God-Class opponents by herself. Behind this side, she's a socially awkward girl who has little more to her desires than the drive to obey the Grandmaster's orders. However, her deep love for her younger sister figure Clare remains as the ultimate trace of her sense of self.

The nature of her strength comes from her unparalleled ability to sense aura and power flow. Despite being apparently human, Niphelia has swordsmanship skills that completely outclass Aslatiel's, magical power beyond Asura's and enough physical strength to kick away Vali in his Balance Breaker state. Her partner is Asura.

No.2 Shimadal
The last Seraph-Class Angel created by the God of the Bible, Shimadal is anything but an exemplary Seraph. Designated as the Angel of Curiosity upon his creation, Shimadal found at some point a loophole in the System of Heaven, and upon tampering with it, he has become able to freely engage himself in debauchery and evil acts without falling.

His main strength lies in his resourcefulness and intelligence, being a scientist on par with Azazel and having cunning on Cao Cao's level. In terms of combat skills, he's equal to a Satan-Class Devil, but he prefers to solve things in what he calls "diplomatic" ways, which can range from blackmail to bribing and kidnapping. His partner is Aslatiel.

No.3 Dirk Eberwein
A scythe-less Grim Reaper, Dirk is still one of the strongest members of Stigma in terms of combat ability. While somewhat similar to Shimadal in terms of being particularly reliant on their cunning, Dirk is much more likely to resort to battle during most ordeals. Being a talented mage as well, he also maintains a teacher-student relationship with Airi.

Nicknamed "Tyrant", he's one of the few Grim Reapers who have disobeyed Hades' authority and lived after it. The true extent of his powers is even beyond that of a Satan-Class Devil. His partner is Lurie.

No.4 Rama
A descendant of the heroic avatar of Vishnu, Rama is a considerably strong battler who has inherited the Kodandam bow. He used to be one of the top fighters of the Hero Faction, but left after having a dispute with Cao Cao over who should be the leader.

Despite being a member of Stigma, Rama has an unusually strong moral code and will reject any order that goes against his principles, even if it comes from the Grandmaster himself. He gets along well with both Aslatiel and Asura.

Rama is a masterful archer who can even hit targets moving at the speed of sound, but is no good at other methods of fighting by his own admission. His partner is Aksel.

No.5 Airi Vollan
The youngest among all Stigma members, being merely fifteen years old. Despite being little more than a child, Airi is a prized member of Stigma due to her uncanny magical talent, being a user of even lost magic outside of Merlin Ambrosius' system.

Just like Aslatiel and Dante, she has the ability to communicate with Spirits, but hasn't made a contract with one yet. She's able to fly without any kind of wings and is able to restrain Aslatiel in his Black Armor. She appears to have romantic affection towards Asura. Her partner is Dante.

No.6 Asura
The Demi-God son of Shiva, the God of Destruction, and Aslatiel's self-proclaimed best friend. Just like Niphelia, he's ranked only in accordance to his combat power, which is one of the highest among the whole group.

Upbeat and cheerful, Asura is unusual among Stigma members, but most appear to enjoy his role in cheering up their usual brooding selves. He gets along well with Rama and Airi, but seems unaware of the latter's attraction towards him. His partner is Niphelia.

No.7 Aslatiel Bael
A Pure-Blooded Devil from both the Bael and Marchosias Devil Clans. Aslatiel's main characteristics are his combat prowess and his ability to communicate with Spirits, having a contract with the strongest Steel Attribute Spirit, Terminus Est.

Due to his smooth success in a deal with Japan's largest multinational company, Aslatiel is also a main actor in Stigma's financial affairs. He gets along well with Lurie and Rama, while also being Niphelia's main conversation partner.

Aslatiel is the only Devil in Stigma, so he's appreciated as their main link to the Underworld. His partner is Shimadal.

No.8 Lurie Lizaldia
Due to her unparalleled regenerative and self-healing abilities, and being able to heal others as well by sharing her cells, Lurie is one of Stigma's prominent members in terms of utility skills.

She's a remarkably skillful spy, and also a capable combatant. She sometimes behaves as the "Older Sister" of some members, such as Aslatiel and Airi.

However, despite her ability to heal from almost any wound in a matter of seconds, her combat power is the weakest in Stigma by her own admission. Her partner is Dirk.

No.9 Dante Agnelli
Known as "God-Slaying Flames", Dante has a contract with the strongest Fire Spirit, Laevateinn. Despite being strong enough just by using its crimson flames, Dante is also an extraordinary swordsman on par with Aslatiel.

Having the most experience as a Spirit user, he sometimes lends advice to both Aslatiel and Airi. He has also shown bisexual tendencies, demonstrating interest in these two.

Dante is the most distrusting of the Grandmaster. His partner is Airi.

No.10 Aksel Jaeger
Nicknamed "Orange Flash", Aksel is a remarkably competitive and hot-blooded fighter. He has a fierce rivalry with Aslatiel, born from the latter defeating him at some point in the past.

Despite being the lowest ranked member, Aksel's combat capabilities are his main specialty and he's stronger than the regular Ultimate-Class Devil. His nickname comes from his incredible speed and agility during battle.

Aksel gets along with Asura and Lurie. His partner is Rama.

Trivia

 * Six members of Stigma are at least part human, while three of those six are full humans.
 * Two members of Stigma are part God. Asura being a Demi-God, and Rama being a descendant of one.
 * While the Grandmaster is the founder, he's not considered an actual member of Stigma.
 * The name "Stigma" comes from the mark of each of the members' and the Grandmaster's eyes.
 * Niphelia's appearance is based off of the Vocaloid Luka Megurine.
 * Dirk's appearance and nickname are based off of the character of the same name in Gakusen Toshi Asterisk.
 * The Grandmaster' and Rama's appearances are based off of Azami Nakiri and Akira Hayama (with loose hair) from Shokugeki no Soma respectively.
 * Asura's appearance is mostly based off of Shuu Iura from Horimiya.
 * Lurie's appearance is based off of the character of the same name in Seirei Tsukai no Blade Dance.
 * Dante's appearance is based off of Sousei Abeno from Donten ni Warau.
 * Aksel's appearance is based off of Shun Iriya from Sugar*Soldier.