Solomon's gate

Solomon's gate(魔剣の王国; Soromongēto; lit. "Kingdom of the magic swords") was an mass-product artificial Sacred Gear created by former fallen angel governor General Azazel, to help members of the Three factions alike to store and repair great quantities of weapons in it during the Great Apocalypse. Nowadays, this Sacred Gear is of exclusive use of one of the current Satans, Cohen Lucifer, and whoever is 'worth' it's use.

Unlike normal Sacred Gears, Solomon's Gate can be shared and even given to other users, making it more of an item than an ability. However, power compactibility is needed for such, as some users cannot summon high-tier demon/holy swords if they're not strong enough.

Summary
Solomon's gate was one of the last inventions of the Fallen Angels Governor General Azazel, created for the purpose to store demon/holy swords in case more or new ones are needed at the heat of a battle. As time progresses, however, new ways of using Solomon's Gate were created to further improves one's performance in battle.

After the Great Apocalypse, Solomon's Gate users fused their abilities in a single, exclusive one, giving it to the strongest user at the time, Cohen Alastor. The amount of swords inside of it can be considerate an alternative dimension, full of demon swords from the lowest tier to the strongests, apocalyptic ones.

Appearance
This Sacred Gear has no physical form, instead manifesting itself in magic circles around the user, from which demon swords' handles appears for the wielder to pull it out of their dimension.

Abilities
Being a support type of Sacred Gear, Solomon's Gate works in a way similar to a Bag of Holdings, storing swords in a pocket dimension for later use. While being able to store every kind of sword, a magical security lock prevent users from pulling swords too powerful for them to control, i.e., a low-class devil can't pull a high-tier sword. While not in use, the swords are stored in a pocket dimension full of magical energy, where they're repaired by absorving it.

It can also work as a long-distance weapon, as swords can be launched at high speeds to either assists an disarmed ally or work as a projectile to harm foes. A running gag is that it can store other things besides swords, as Aria pulled a jar of wine and Cohen ended up lauching adult magazines while using Reloaded. However, due to the energy-filled environment of the sword dimension, there's the risk that non-sword objects might get consumed or destroyed by it.

It's noted that, while the Sacred Gear can repair broken magic swords, it can't create them.

Forms
The standard form of Solomon's gate is of several magic circles around the user, which sprouts sword's handles for it to pulled it out of the pocket dimension. The number of circles that it can form is proportional to the current level power of the user. The stronger the user, the higher the number of circles it can create.

Solomon's Gate: Reloaded(ソロモンゲート: リーローディッド; Soromongēto: Rīrōdiddo) - A more offensive form, he user creates a wall of magic circles by it's back and launches several swords with their blades pointed to the target. The speed, power and number of magic circles is also proportional to the level power of the user, as Cohen Lucifer, an ultimate-class devil and Satan, can summon countless swords and launch them at high speed, similar to a machine-gun.

Solomon's Gate: Revolution(ソロモンゲート：レボルーション; Soromongēto: Reborūshon) - Possibly Solomon's Gate strongest form, it can only be archieved when the user is strong enough to subdue all of the sword's powers combine. With it, the user can take foes to the realm where the swords are stored, and they can only get out when the user allowed them to, or when it's either killed or with the power level below accepted by the blades. Since it was originally created to home nothing but swords, the pocket dimension takes the form of a wasteland in eternal dawn, with several swords stuck on the sandy ground. While at it, because of the complete synch between the user and the blades, any intruder that try to take a sword for itself will be rejected by it. Solomon's Gate: anima(ソロモンゲート：アニマ; Soromongēto: Anima) - Being a descendant of the Alastor clan, a nomad clan of extra devils masters in beast-taming, Cohen Lucifer is capable to create a section in Solomon's Gate's pocket Dimension for his familiars and beasts. This technique can be considerate exclusive of his, as no other devil can summoned them without extra help, and if they ever do it, the beast will be too strong for them to control it. Just like the swords, the beasts can be healed in the pocket dimension, but they can not recover from things like fatigue, stress or sleep.

Trivia

 * The name of the Sacred Gear, as well as some of it's images, are named based on 'Gates of babylon', a technique by Type-moon's character Gilgamesh. Other images includes Archer's'Unlimited blades works' and Arata Kasuga's transformation sequence.
 * While he can remember the exact number of swords, Cohen stated that the quantity is already near eleven digits.
 * A skit reveals that the Sacred Gear can store other things besides familiars and swords, like jars of wine and adult magazines.