Twilight (黄昏, Koukon) is the title given to the children and descendants of those who used theCelebre 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 "Tagged". 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.