Asmodeus

Asmodeus (アスモデウス, Asumodeusu) also known as the Demon Sword, is a Cursed Sword that has been passed down through generations of The House of Flaming. It is currently carried by Arnest Flaming.

Appearance
Asmodeus has a unique design. Its edges are waves composting to the bevels, with the flat contrast between the two individual halts in steel. The halt almost connects to the two large and oddly shaped points of the symmetrical blade leading to cross stamped middle that protects the wielder while their hands rest on the leather handle. It's sheath is also composed of black leather with bronze finishing.

Overview
Asmodeus is the treasure of the House of Flaming, as it has been passed down for generations, from ancestor to another. It was the blessing of the house while it was sealed. The wielder of the sword becomes the next head of the House of Flaming. The sword's curse sometimes turns it's wielder's hair to red or vermilion in Arnest's case.

Asmodeus is possessed by a demon, able to manifest itself before the wielder in a form of black smoke and speak to them, though it is unknown if others can see and/or hear it as well in that state. However, once inside the sword's world, the demon Asmodeus manifests himself in his true form. The demon would entirely possess the wielder if they don't have an iron will to fight it, something that the Flamings' conveniently developed.

History
Asmodeus has been passed down through generations of the House of Flaming, the last being Arnest. It was sealed for an unknown period of time before Arnest released its seal and became the new owner. The sword was chained inside a dark room somewhere within the Flamings' household.

Transfer Student arc
Years later Arnest is seen carrying it around with her all the time. While she was in the restrooms, it manifested itself to her only to be quickly sealed back in. The sword raises Blade's suspicion and he asks Arnest about it, only to be turned down by the latter. The demon appears to her again and tells her that they should dispose of Blade because "He's dangerous" but Arnest calmly defies it and the demon disappears once again.

Trivia

 * Asmodeus' name is a clear reference to the mythological King of Demons, Asmodeus.
 * It's possible that the sword took a special liking to Arnest as she is only the second wielder of the sword to have their hair color changed.