The Emperor (エンペラー) is a mysterious man operating as a high-ranking member and Warden of a certain Organisation.
Emperor exploits low-ranking members of his organisation as tools and ruthlessly murders anyone daring to escape the organisation. He wears a golden artifact, called the Monarch's Regalia in the novel, that allows him to manipulate gravity and has crushed numerous bodies under overwhelming gravity.
After learning that the Nine of Swords appeared to betray the organisation, the Emperor was lured out to confront the traitor. He did not know that her partner, the Three of Swords, was also in on the plan. He was killed in the ensuing battle.
A simulacrum of him appeared to assist Supreme Leader Rufus Albarea. Like his namesake, the simulacrum bore most of the Emperor's personality, appearance and equipment. However, rather than purging traitors, he sought to bring back the traitors, Nadia and Swin.
The simulacrum only learned that he was a fake when Nadia was able to discern glaring flaws that confirmed her suspicions about him. Regardless, he chose to surpass his original upon learning of this, but was ultimately defeated by Nadia and Swin, alongside the rest of their group. Following his defeat, his replicated artifacts resonated with him, transforming him into a monster. He ambushed the group once more at Crossbell's police academy, but was defeated for good this time by the pair.