Arch-Enemy Event Weapon

The Nox Nyctores Causality Weapons (事象兵器アークエネミー), also known simply as Nox Nyctores and the Causality Weapons (事象兵器), are a set of eleven weapons, and the final stage of Ars Armagus. The first ten were tempered as a set of close range and melee-type weapons to directly oppose the Black Beast. An advanced tempering technique was needed to forge them, and a total of ten weapons were planned.

Information
The first nine were created during the First War of Ars Magus to combat the Black Beast. They were based on the Sankishin. Only those with the highest proficiency in the proper use of Ars Magus can wield them, and even then, there is a significant risk of mental burden on the user. It is said that the Nox Nyctores choose their masters. Just like magic attacks, they also cause scarring of the soul.

One of the primary functions of Nox Nyctores is to unburden their owners of "needless" emotions and enhance others; this has a profound effect, for example eliminating fear, but owners may also find themselves losing their compassion, remorse, etc. Strong-willed individuals such as Hakumen and Jūbei seem to be highly unaffected by this side-effect, however.

While being powerful enough to fight the Black Beast, Nox Nyctores are affected by the Boundary. If a Nox Nyctores with a released core is put near the Cauldron, its ability cannot be activated.

The catalyst to smelt a Nox Nyctores are human souls. To create a Nox Nyctores is required smelting an artificial identity (擬似人格) deep within the Boundary, it is able to observe itself and refine its existence. The stronger the observation, the stronger its value as a weapon it becomes. Depending on whether it takes the observation multiple or individual ways, is what determines its viability as a weapon. Observing its soul in multiple ways would make it more effective as a weapon, enabling it to make multiple observations simultaneously. The core's smelting process involves compressing the seithr (Seithr Fluid Body Theory) into its threshold limit, forming a unit, and is then implanted with a "soul". In concept, this process is similar to smelting the core of a causality weapon.

The core of a Nox Nyctores is the Black Beast itself. Back during the Dark War, Konoe A. Mercury had to create her own Black Beast, compress it, and seal its soul. She was able to do it by a magic spell, Infinite Gravity. The sealed Beast is compressed into the size of an apple. Then, the compressed Beast can be used as the catalyst for the newly created Nox Nyctores number 1, Gigant: Takemikazuchi. The core of Takemikazuchi was divided and used in the weapons number 2-9. The 10th Nox Nyctores, Lux Sanctus: Murakumo, is unique in that it was produced after the First War of Ars Magus and it doesn't have Takemikazuchi's core.

There are also imitation Nox Nyctores called Artificial Causality Weapons. They rely on atomic power instead of the life energy (human souls) used during the forging of the Nox Nyctores. They are replicas, but have comparable power and are recognized by the Nox Nyctores as being similar. Jūbei once experienced a resonance created by his Mucro Somnio: Musashi when it came into contact with one. There is an upgraded version of the artificial causality weapon known as the Idea Engine, but nothing else is known of it.

List of all known Nox Nyctores

 * 1) Gigant: Takemikazuchi (・タケミカヅチ) — A giant humanoid, who later was sealed within a satellite and sent away from the world. Eventually it was turned into the Embryo. Its core was used for the Nox Nyctores number 2-9. It was wielded by the Takamagahara System, and also temporarily by Hades: Izanami.
 * 2) Mucro Algesco: Yukianesa (氷剣・ユキアネサ) — A katana with the blade made of ice. It is wielded by Jin Kisaragi, and previously by Seven.
 * 3) Arcus Diabolus: Bolverk (魔銃・ベルヴェルク) — A pair of handguns with the power to pierce through space. It is wielded by Noel Vermillion, and previously by Three.
 * 4) Deus Machina: Nirvana (機神・ニルヴァーナ) — An automaton with a female appearance. Nirvana has her nails made of a material that negates Ars Magus. It is wielded by Carl Clover, and previously by Celica A. Mercury.
 * 5) Mucro Somnio: Musashi (夢刀・六三四) — A pair of kodachis. Musashi's power is to cut "what cannot normally be cut". It is wielded by Jūbei.
 * 6) Interfectum Malus: Ōkami (斬魔・鳴神) — A nodachi with the blade made of a metal that negates Ars Magus. It is wielded by Izayoi, and previously by Hakumen.
 * 7) Arma Reboare: Muchōrin (雷轟・無兆鈴) — A wand that appears to be as long as its wielder. Its abilities are the incarnation of matter. It was wielded by Trinity Glassfille, and then Platinum the Trinity. It is unknown what happened to Muchōrin after materializing the latest thing, Hihiirokane weapon.
 * 8) Geminus Anguium: Ouroboros (蛇双・ウロボロス) — A never-ending chain with a snake's head. It can cause direct damage to the victim's mind. It is wielded by Hazama, also by Yūki Terumi and previously by Kazuma Kval.
 * 9) Phoenix: Rettenjō (鳳翼・烈天上) — A giant 55-inch nail. It is an Anti-Nox Nyctores weapon, and the core of Kushinada's Lynchpin, which has the ability to stop the functionality of seithr. It is wielded by Bang Shishigami.
 * 10) Lux Sanctus: Murakumo (神輝・ムラクモ) — A large sword which transforms into the armor and eight floating blades. This weapon was created after the Dark War, so it is the only Nox Nyctores without a part of Takemikazuchi's core. This type of weapon is wielded by the Murakumo Unit.
 * 11) Corpus Sepulcro: Requiem (骸葬・レクイエム) — A giant humanoid. It was made to replace the Amaterasu Unit, and create the new world that is not based on Amaterasu's dreams. Requiem was supposed to serve as a new god, a perfect system which doesn't have emotions, so the world would not have the Phenomenon Interventions. This weapon wasn't completed, and eventually was destroyed.

Trivia

 * This set of weapons is called in the Japanese version as Arch-Enemy Event Weapons. An "arch-enemy" is the principal enemy of someone or something.
 * This set of weapons is called in the English version as Nox Nyctores Causality Weapons. "Nox Nyctores" is a term made of three words: "nox" – Latin word for night, "nycto" – Greek word for night, "res" – Latin word for thing.