The Gentlemen Thief Empire are a criminal society who steals in the name of being a Gentlemen Thief hence are the rival of Milky Holmes who represents the detectives of law and order. Their leader is Arsene, whom her loyal servants call Lady Arsene. Under the alias Henriette Mystere, Arsene is disguised as the student council president of Holmes Detective Academy.
Their targets are usually gems and or treasures of great value. They hold great pride in their actions executing withh style and beauty, never resort to using brute force and mass destruction as a means of accomplishing their goals. But since Milky Holmes girls has lost their Toys, they are now unrivaled in Yokohama save for the G4 police force who is always bested time and again. For that reason, unbeknownst to her minions Arsene tries to make them recover their Toys and fight them again.