Demon Guns: Bolverk (魔銃・ベルヴェルク Majū: Beruveruku, localized as Arcus Diabolus: Bolverk) is an Arch-Enemy Event Weapon in the shape of a pair of handguns. It is the main weapon of Noel Vermillion, and previously was wielded by Three.
A weapon that pierces through space, detonating an Magic Formula-based blast wherever one aims it. Bolverk can attack targets through walls, Type XI: Optic Barrel being a dimensional collapse of sorts at a point in line with the barrel. It also serves as a limiter for Noel as it suppresses her emotions, explaining why she does not become emotionally unstable, unlike Carl Clover or Jin Kisaragi. It is also revealed that in Noel's past, while she was being attacked by a monster, Bolverk appeared suddenly right before her. Noel's emotions can break Bolverk, unleashing her true persona. Bolverk is later restored – it is unknown how it happened.
During the Great Dark War, Bolverk had a multitude of owners, including Three of the Ten Sages. After their death, Bolverk was given to so many owners over time, its location eventually became unknown to even Jūbei until its possession by Noel Vermillion.