Brown Bess appears as a teenage male with fair skin, blonde hair reaching his ears featuring distinct sidelocks, and green eyes. Standing 175 cm (5'9") tall and weighing 58 kg (128 lbs), he often displays an irritable scowl or glare, though blushing is also depicted. He represents the historical British Army "Brown Bess" musket, embodying its 18th-century origins and role in conflicts like the American Revolutionary War, where its notorious inaccuracy from undersized bullets necessitated battalion volleys.

Personality-wise, he adheres strictly to a knightly code focused on protection and duty, claiming his actions stem solely from pride as a British knight and service rules, explicitly denying deeper sentiment. He exhibits a proud, occasionally tsundere demeanor, dismissing protective actions as mere obligation. He favors black tea and rock music, pursuing guitar as a hobby.

Belonging to the American Revolutionary War group within the narrative, Brown Bess is an anthropomorphic manifestation of the antique firearm. As a Noble Musketeer, he fights the World Empire in a post-nuclear dystopia alongside others repurposing historical weapons. In combat, he demonstrates supernatural capabilities beyond a normal musket, including rapid firing of energy-like projectiles. The character features in the main anime series and the OVA "Kijūshi-tachi no Happy Birthday!".