Twenty, operating under the alias Kai Nijuuri, serves as one of the Three Cards within the Thieves' Empire, answering directly to leader Arsène. He possesses blond spiky hair with distinctive bangs, piercing blue eyes, a pale, slim physique, and a noticeable mole. During undercover missions, he dons formal attire: a suit, necktie, gloves, hat, and monocle.

His codename, Twenty, alludes to Edogawa Rampo's Fiend of Twenty Faces. As a magician-thief, he executes heists utilizing specialized tools like cards, flying machines, and various trick devices. His supernatural Toy ability grants him flawless disguise, enabling seamless infiltration. This power underpins his double life, allowing him to gather intelligence while posing as a teacher at Holmes Detective Academy.

Twenty exhibits a blend of pronounced narcissism and overt perversion. He carries a personalized bolster featuring his own image for comfort and routinely engages in attention-seeking antics, including stripping and deliberately exposing his erect nipples during both thefts and classroom sessions. These behaviors function as recurring comedic elements but also render him an ineffective instructor, causing students to frequently ignore him or zone out during lessons.

His background origins, character development across media, and specific narrative evolution beyond his established role remain undefined. His undercover position at Holmes Detective Academy is consistent, with no documented shifts in allegiance, core motivation, or fundamental abilities throughout official media.