Joker serves as a primary assistant to the Phantom Thief Queen, operating alongside her and an AI entity named RD. They execute elaborate thefts globally while traveling aboard the airship Troubadour. During the events of "Kaitō Queen wa Circus ga Osuki," Joker supports Queen’s pursuit of the cursed Rose of Linden gemstone. When the circus troupe White Forest steals the jewel, Joker aids Queen in confronting the troupe’s hypnotists, magicians, and acrobats to reclaim it. Their collaboration proves essential to overcoming these challenges and achieving Queen’s objectives. Joker’s role remains strictly defined as Queen’s supporting accomplice within these documented events.