Demon Sword

The Demon Swords are swords forged by the orignal Satans.

Summary
Not much is about about the the Demon Sword except that Demon Swords have a strong curse placed on them and brings misfortune to its wielders. All five Demon Swords were wielded by Siegfried of the Hero Faction. In Volume 12, one of the five Demon Swords, Gram, left Siegfried and chose Yuuto Kiba as its new wielder, allowing Yuuto to defeat Siegfried. Following Siegfried's defeat, the remaining Demon Sword chose Yuuto as their new wielder as well.

Abilities
They are the exact opposite of the Holy Swords, in which they use demonic powers and are extremely powerful against Angels. Just as with the Holy Sword, only a selected few can wield Demon Swords. Demon Swords appear to have a form of will of their own, as revealed in Volume 12.

Gram
Gram (グラム Guramu), also known as the Sword of the Sun, is the strongest Demon Sword. Known as the Demonic Emperor Sword (魔帝剣 Mateiken), it is a Dragon Slayer sword with the destructive power of the Holy Sword Durandal, which causes Yuuto to compare it to a combination of Ascalon and Durandal, but does not need to be charged to do destructive attacks. It was previously used by the original Siegfried to slay the Dragon King Fafnir (though Fafnir was later revived by the Norse Gods).

Balmung
Balmung (バルムンク Barumunku) is a Demon Sword with a drill-like aura.

Nothung
Nothung (ノートゥング Nōtungu) is a Demon Sword that can rip through space-time.

Tyrfing
Tyrfing (ディルヴィング Diruvingu) is a Demon Sword that can create craters.

Dáinsleif
Dáinsleif (ダインスレイヴ Dainsureivu) is a Demon Sword that creates huge pillars of ice from the ground.

It is possible (under certain conditions) for a Holy Sword to become a Demonic Sword, as with the case of Arondight.

Trivia

 * All Demon Swords (except Arondight) are named after swords used in Norse mythology.
 * Balmung and Nothung are alternate names for Gram.
 * Dáinsleif, meaning "Dáinn's legacy" in Old Norse, was a sword wielded by King Högni in Norse mythology.
 * Tyrfing is the titular sword used in the Norse legend collection the Tyrfing Cycle. According to the legend, it was a sword forged by the Dwarves Durin and Dvalin. They are forced to do so by Scafrlami, the king of Gardariki, but in revenge they curse the sword so that it will kill a man every time it is unsheathed, cause three evil deeds and be the undoing of Svarflami.
 * Arondight is the name of the sword used by Sir Lancelot, one of the Knights of the Round Table in Arthurian legend.
 * Gram is so far the only demon sword that has two abillities: dragon-slaying abillities and destruction abillities