Murr is a white Persian cat with long, silky fur and a noticeably chubby physique. His most distinctive feature is his heterochromatic eyes—a purple right eye and a blue left eye—mirroring the enigmatic Teacher. He consistently wears a purple ribbon collar with a round jewel at its center. Originally owned by Louis de Sade during Noé Archiviste’s childhood in Averoigne, Murr lived with Louis, his grandfather the Teacher, and Noé. After Louis's death, Murr became Noé’s primary companion, accompanying him to Paris when the Teacher tasked Noé with investigating the Book of Vanitas. Murr exhibits a perpetually grumpy and irritable demeanor, often frowning and scratching Noé when displeased. Despite this, he tolerates Noé’s company and frequently perches on his shoulder. He shows a clear preference for women over men, eagerly seeking attention from figures like Amelia Ruth. Murr displays unexpected fondness for Vanitas, occasionally sleeping on his lap—behavior Noé finds puzzling. He also develops a crush on Flute, a black cat at Hôtel Chouchou, though she remains indifferent. His longevity is notable, appearing unchanged from flashbacks over a decade earlier. While primarily a companion, Murr demonstrates intelligence, such as escaping his carrier to approach Amelia. He forms positive relationships with characters including Count Orlok and his assistants Nox and Manet, who dote on him after initial rough handling. A recurring theory suggests Murr may be more than an ordinary cat. His matching heterochromia and the Teacher’s remark to Vanitas about meeting "in a different form," combined with Murr’s unexplained longevity and the Teacher’s shapeshifting abilities, fuel speculation that Murr could be a physical manifestation or familiar of the Teacher, potentially acting as his eyes to observe Noé and Vanitas.