A brilliant detective whose face is shaped like a butt. He is always calm, collected, and acts like a perfect gentleman. He speaks politely and his catchphrase is "Hmm, I smell trouble." In this story, to investigate a disappearance, he goes undercover as an idol to infiltrate a contest. In the end, he unleashes a powerful finishing move to stop a plot to destroy the world.

A small dog who serves as Butt Detective's assistant. He is pure, honest, and a bit prone to getting carried away. He speaks in a dedicated, polite manner. In the movie, he supports the undercover investigation in idol attire and plays a major role following in Butt Detective's footsteps.

A legendary thief of the century. He has a flamboyant appearance, wearing a large poop-shaped hat, a black cape, and a white tuxedo. He loves everything stylish and his catchphrase is "Très bien!" In this work, to recover the stolen secret "Moonlight Stone," he forms a temporary, forbidden tag-team alliance with his arch-rival, Butt Detective.

The boss of the criminal organization "Thief Academy" and the true mastermind. He has an eerie appearance, looking like a fat cockroach shrouded in a black silhouette. He is greedy, cold-blooded, and loves hoarding money. He is the villain behind the "Dark Age Project," which aims to cover the world in darkness. He actually has a past connection with Master Thief U.

A masked female thief with a bat-like appearance. She fervently seeks treasures that will make her shine even brighter. She usually disguises herself as a commoner. She is actually an old acquaintance (childhood friend) of Master Thief U and is a crucial character who knows his hidden past.

A thief with a crow-like appearance. He is a massive collector of gemstones. Having been fired from the Thief Academy in the past, he operates independently while harboring a strong resentment toward the organization.

The intellectual thief in charge of technological development for the Academy. With the appearance of a genius scientist, he invents gadgets and new weapons for the thieves one after another. He supports the systems of the Dark Age Project from the shadows. He is Brown's long-lost twin sister.

Appearance: Characterized by a large build, a thick neck, and drooping eyes. Personality/Role: A hot-blooded, combat-oriented detective. He puts his body on the line to face incidents head-on.

Appearance: As the name suggests, he is characterized by his fluffy, permed hair. Personality/Role: A slightly pretentious detective who looks sharp in a trench coat.

Appearance: Characterized by perky, pointed ears and narrow eyes. Personality/Role: A calm and sharp-witted detective. He supports investigations with his keen powers of observation. These three work under Chief Maltese, cooperating with Butt Detective to protect the peace of the town.