Rhongomiant

The Holy Ghost Sword Rhongomiant(無形聖剣ロンゴミアント; Mukei seiken rongomianto) is one of the first holy swords ever crafted by the God of the Bible, being one of King Arthur's swords, overshadowed by the more known Excalibur.

Being forged with early alchemy and being blessed by several other deities, it's because of said blessings the sword became unable to fuction as a true holy sword, then receiving the name of "The Failure". Currently, it's being held by the current Host of the Boosted Gear in the Highschool DxD: Яe-birth continuitity, Ichijou Tsukino.

Summary
Considered one of the oldest holy swords ever crafted, Rhongomiant was one of King Arthur's swords, overshadowed by the more known Excalibur. Crafted with blessed Lapis-lazuli as the blade, bathed on tears of holy maidens wailing for their Lord on the hilt and with several magic runes crafted on the edges, thus making them dull and non-cutting. However, because of such number of blessings, the sword ended up saturated with power, and thus became unable to fuction as a normal holy sword because of it, with all the blessing nullifying themselves from within.

The sword was considered a failure, and thus banished from history. Millenias after, King Arthur would receive such blade, which was being guarded by the Lake Fairy, becoming one of it's blades.

Appearance
Rhongomiant takes the shape of a large broadsword, roughly with 2 mt. in height, with a golden blade decorated with lapis-lazuli shapes on it's edges and hit. There is no pointer and the edges are dull due to several magic enchantment words crafted in it, thus unabling it to cut anything. Before he starting using it, Ichijou noted that by the end of the hilt, there was a ribbon wrapped it around it, belonging to the late Akeno Himejima.

Abilities
Despite being a failure sword, Rhongomiant still retains the ability to purge and scare lesser demons away. The aura around it is extremely subdue for devils, yet deadly for lesser beings, like ghouls and evil wanderer spirits. Also, because of it's saturated blessings and power-ups, the blade is innofensive and can be used and chosen by devils and humans alike. For being a broadsword, it can also damage grounds and foes with an absurd destructive force.

Trivia

 * The image in question for the sword is based on Avalon from the FATE/Zero series.