Rat, alias Jirō Nezu, stands as a primary antagonist within the narrative. A member of the Three Cards—Lady Arsene’s loyal cadre in the Gentlemen Thief Empire—he operates under dual identities: a phantom thief and an undercover student at Holmes Detective Academy, masquerading as a classmate to the protagonists.

His pyrokinetic ability, dubbed his “Toy,” grants him mastery over flames, primarily channeled to detonate explosives during heists for both offense and defense. Energetic, aggressive, and hot-tempered, his demeanor parallels Nero’s confrontational zeal among the protagonists. Though he maintains a cold, aloof persona at the academy, subtle hints of unspoken care—particularly toward Nero—linger beneath his guarded exterior.

A running gag sees the protagonists consistently botching his alias, dubbing him “Rabbit” or “Rising Thunder” instead of Rat—a humorous reflection of his precarious undercover status. Even when employing his Toy during missions, his true identity as a phantom thief stays concealed, as the protagonists remain oblivious to the clues in plain sight.

The Summer Special narrative shifts focus to other characters, leaving his activities during that period uncharted. Broader media iterations reinforce his role as a secondary antagonist embedded within the academy, adhering strictly to his established traits without expanding on his backstory or personal evolution.