Twenty, operating under the civilian alias Kai Nijuuri, is a core member of the Gentlemen Thieves, a group led by Henriette Mystère within the expansive Thieves' Empire. His codename draws inspiration from Edogawa Rampo’s "Fiend of Twenty Faces," aligning with his expertise in crafting impeccable disguises to infiltrate high-security targets. As part of his covert role, he maintains a dual identity as a faculty member at Holmes Detective Academy, leveraging his position to advance the Thieves' schemes while evading suspicion.

His signature ability, derived from a specialized Toy, allows him to adopt flawless personas, enabling seamless access to restricted areas. Complementing this skill, he employs stage magic techniques—utilizing trick cards, mechanical gadgets, and theatrical flair—to execute missions. Known for flamboyant narcissism, he carries a self-printed bolster for emotional support and habitually disrobes mid-operation to assert dominance, a trait that bleeds into his teaching persona. Despite attempts to captivate students with dramatic antics, his efforts often result in indifference or classroom chaos.

Though primarily a source of comedic relief—marked by quirks like reactive erogenous zones during adrenaline spikes—he remains a tactically astute operative loyal to the Thieves' Empire. His narrative function pivots on antagonizing protagonists, notably by reigniting their abilities to ensure "worthy" rivalries. The situational irony of his undetected dual identity persists, as main characters overlook behavioral parallels between Kai and his Twenty persona.

Canonical materials establish his faculty position as a calculated cover for espionage, though his origins prior to joining the Thieves remain undefined. Spin-offs and alternate universes preserve his core traits, reinforcing his recurring role as a theatrically inclined adversary whose blend of absurdity and competence sustains narrative tension.