Twilights

The Twilights (黄昏,) are title given to the children and descendants of those who used the Cerebret drug. While Ergastulum was created to control and house Twilights due to an influx of them after the war, they are still a source of controversy. Anti-Twilight factions are prominent in the city despite pro-Twilight support from three of the four Big Fathers.

From birth, they are registered and controlled using tags embedded with chips that monitor their vital signs. Thus, they are also known as "Tags". These tags also have their rank - speculated to be a measure of the Twilight's strength - with D/5 (the default) being the lowest and S/0 the highest. After a Twilight's confirmed death, they are automatically deleted from their category and their family registration. Every record of their existence is erased."​"

Ranks
Twilight ranks from highest to lowest:
 * S/0, S/1, S/2, S/3, S/4, S/5
 * A/0, A/1, A/2, A/3, A/4, A/5
 * B/0, B/1, B/2, B/3, B/4, B/5
 * C/0, C/1, C/2, C/3, C/4, C/5
 * D/0, D/1, D/2, D/3, D/4, D/5

When a ​Twilight achieve a certain number of kills or is otherwise deemed sufficiently powerful enough to advance, his or her rank will be promoted

The Three Laws
Twilights are required to follow three laws:
 * The First Law: Twilights shall not deliberately harm any human. Nor shall they allow a human to come to harm through inaction.
 * The Second Law: Twilights must obey any order given to them by a human. The only exception being if that order conflicts with the first law.
 * The Third Law: Twilights must protect themselves, so long as such protection does not conflict with the first or second laws.

Biology
All Twilights possess enhanced abilities due to their predecessors' use of Celebrer. They are noted for being incredibly violent and destructive; Twilight mercenaries are often hired due to their effectiveness in battle and one of the four big houses, the Paulklee Guild, offers its Twilight members as hired guns. It is speculated that Twilights are grouped into certain "types" depending upon their forté. Marco observes that, like Galahad, Mikhail seemed to be a "power-type", and Ginger is noted for her incredible speed.

However, Twilights are riddled with sometimes multiple mental and physical disorders, known as "compensation", which is hereditary. Along with these deficiencies, the lifespan of a Twilight is drastically shortened, usually ending in their early thirties. There are more cases of severe compensation with those who have a Twilight mother as opposed to those with a Twilight father.

Hagure (日暮れ) is the title given to the children of a Twilight and a normal human. They have less severe compensation, less required intake of Celebrer and slightly longer lifespans due to their normal parent. There are records of some living to be 49 years old.

Rank D
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Trivia

 * The three are inspired by Isaac Asimov's Three Laws of Robotics.