D or Type Dragon is a type of human that was born after the first dragon disaster engineered by 'Black' Vritra 25 years before the events of the story. Their defining characteristic is their ability to generate and manipulate dark matter, a trait which originated from Vritra's Authority, and they play a central role in the events of Unlimited Fafnir's history.
A D's power manifests for the first time during the development of the secondary sex characteristics and disappears completely around the age of twenty or if the D becomes pregnant, in which case their powers gradually disappear over the course of three months. According to Vritra, this occurs because once their bodies mature, they can no longer synchronize with Counterdragons, since the purpose of the Ds' power is to evolve their bodies into those of Counterdragons.
Almost all known Ds are females, with the sole exception of Yuu Mononobe, the world's only male D. A unique characteristic of Ds is the existence of the dragon mark, a symbol that is engraved on some part of their bodies and resembles a dragon. The size of the dragon mark indicates how much dark matter a D can generate and changes color when a Counterdragon has targeted a specific D. If a D, whose dragon mark has fully changed, makes contact with the Counterdragon who targeted her, then she will change into a Counterdragon of the same type, as was the case with Miyako Shinomiya.
According to Vritra, the creation of Ds was part of her plan to have the human race evolve into an existence similar to Counterdragons by having the first generation Ds breed with Counterdragons until the third generation is born, which will be able to pass on its powers even when mating with ordinary humans. Vritra's objective had been to strengthen life on Gaia in preparation for the arrival of the Ninth True Dragon, who has the power to destroy the world.
As was mentioned before, Ds are defined by their ability to generate dark matter, an unknown substance that has been speculated to have originated from a higher dimension, and transmute it into various forms, with most Ds being able to generate an amount close to 10 tons. Most Ds channel their power through Fictional Armaments, weapons created from the imagination of the wielder by maintaining their dark matter into the shape of a weapon. If a Counterdragon is defeated by a D, it is possible for the D to inherit its Authority, as was shown with Mitsuki Mononobe, Iris Freyja and Yuu Mononobe. However, a D who inherits an Authority can also change into a Counterdragon, as was shown with Iris.
The first Ds started appearing shortly after the first dragon disaster 25 years before the events of the story. At first, because of their ability to transmute dark matter into any kind of resource, wars were fought over their acquisition between various countries. Eventually, the United Nations labeled Ds as a resource belonging to the entire world under the management of the international organization Asgard. NIFL, Asgard's military branch, then proceeded to capture Ds all over the world under the pretext of protection, isolating them on a remote island called Midgard.
However, as time passed by and the Ds grew up, they began to petition for their rights as humans. After the awakening of Firill Crest, the granddaughter of the king of the Principality of Erlia, Albert Crest, as a D, things changed, with King Albert using Erlia's widespread influence to transform Midgard into a school for teaching the Ds, as well as starting a movement which restored the Ds' human rights. Ds then became essential to society by using their powers to produce scarce resources, especially mithril, a metal alloy which could only be synthesized by dark matter transmutation. Ds also became humanity's trump card against the Counterdragons, since only their abilities could actually harm them. However, there are Ds around the world who actively use their powers to cause harm to people. These Ds are labelled as 'disasters' and are usually targeted for elimination by NIFL.
- Yuu Mononobe
- Iris Freyja
- Mitsuki Mononobe
- Lisa Highwalker
- Firill Crest
- Ariella Lu
- Ren Miyazawa
- Tear Lightning
- Kili Surtr Muspelheim
- Haruka Shinomiya (formerly)
- Miyako Shinomiya (deceased)
- Shion Zwei Shinomiya (Counterdragon/D Hybrid)