Holy Sword

The Holy Swords (聖剣 Seiken) are weapons forged by the original God.

Summary
There are two types of Holy Swords in High School DxD – the swords of light used by exorcists to exorcise Devils and Fallen Angels, and the True Holy Swords wielded by legendary heroes, such as Excalibur and Durandal. The Sacred Gear Blade Blacksmith has the ability to create Holy Swords but the created Holy Swords are slightly inferior to the real ones.

Abilities
As the Holy Sword uses Holy Powers as its source, it is extremely powerful against Devils and Fallen Angels. A small scratch from Holy Swords are enough to cause lethal damage to Devils and Fallen Angels. However, only a select few can use a true Holy Sword. Holy Swords that are broken can be reforged as long as the core is intact, as shown in the case of Excalibur. It is also possible for two different Holy Swords to be fused into one.

Excalibur
Excalibur is one of the two Holy Swords wielded by the Legendary King of Heroes, King Arthur Pendragon, of Camelot. It was broken in the war long ago and reforged into seven swords through Alchemy and stored by the Orthodox Church.

In Volume 3 of the light novels, Kokabiel and his men stole three Excaliburs from the Church, while four of the Excaliburs were temporarily fused into one by Valper Galilei. The fused Excalibur (wielded by Freed Sellzen) was broken by the combined forces of Yuuto's Sword of Betrayer and Xenovia's Durandal. The broken fragments were then retrieved by Irina back to the Church to be reforged. The Excalibur fragments under the Orthodox Church were later fused into the Durandal as "Control Parts" (制御パーツ) for Xenovia, who is still unable to fully master the Durandal.

Even shattered, the Excalibur Fragments were more powerful than the Holy Swords of Blade Blacksmith, or the Demon Swords of Sword Birth.

The known Excaliburs are Excalibur Destruction, Excalibur Mimic, Excalibur Rapidly, Excalibur Nightmare, Excalibur Transparency, Excalibur Ruler, and Excalibur Blessing. Currently all the Excalibur Swords are fused into the Durandal.

Durandal
Durandal is a Holy Sword that was previously wieled by the Paladin of the Holy Roman Emperor Charlamagne: Roland. Roland had used the sword to fight an army of 100,000 men. It is the main weapon of Xenovia; however due to the sword's immense strength as shown by Roland, she has yet to fully master it. It is a Holy Sword that is said to be on par with the original Excalibur.

Ascalon
Ascalon is a Holy Sword previously wielded by Saint George, the Dragon-killing Saint. Unlike the other Holy Swords, Ascalon specializes in killing Dragons, and is named the Dragon Slayer (龍退治の剣（ドラゴンスレイヤー） Doragon Sureiyā). It was passed to Issei in Volume 4 of the novels by the Archangel Michael as a sign of peace between the three factions.

Caliburn
Caliburn, also known as Collbrande, is the other Holy Sword wielded by King Arthur. The Sword in the Stone known as the Holy King Sword (聖王剣 SeiŌken). It is the most powerful Holy Sword to be created.

Ame no Murakumo no Tsurugi
Ame no Murakumo no Tsurugi (天叢雲剣, lit. "Sword of the Gathering Clouds of Heaven") is a Holy Sword that rivals the Original Excalibur and Durandal. It is also known as the Kusanagi no Tsurugi ("Grass-Cutting Sword"). Unlike the four other Holy Swords, that are said to be forged by God, the Ame no Murakumo no Tsurugi is found inside the body of an eight-headed serpent called the Yamata no Orochi. It has not debuted in the series yet.