Kiln

The Kiln (窯), also called the Yomi Slope (黄泉坂), or the Judgment Gate (裁きの門), formally known as the Sheol Gate (シェオルの門) – also known in XBlaze world as the Yomi Gate (黄泉の門) – is a gate to the Boundary that is used to extract magic element from it.

There is a Kiln under every Hierarchical City, and in all important facilities of the World Void Information Control Organization.

Information
The Kilns are used to access the Boundary, some characters used them to travel in time or between possibilities, and the Arch-Enemy Event Weapons and the Dimensional Boundary Contact Prime Fields are smelted beyond them. It is also possible to smelt a Kiln, but it requires a great number of souls.

A special type of Prime Fields, the Murakumo Units, are smelted in the Kilns. Similarly to an Event Weapon, it takes thousands of souls to create a Murakumo Unit, which explains why the Control Organization branch in the 13th Hierarchical City of Kagutsuchi was completely empty. Hazama had sacrificed the Control Organization soldiers inside the branch so Mu-12 and Nu-13 could be smelted. Smelting a perfect Prime Field, Kusanagi, requires a Murakumo Unit and a Blue Grimoire, which is a portable Kiln which purpose is to gather souls to smelt the sword in its body. The failed merge of a piece of the Blue and a Murakumo results in a Black Beast, but it is also possible to smelt a Beast without using them. According to Relius Clover, the core of the Event Weapon is actually a compressed Black Beast.

Nu was smelted in the Kiln at the bottom of Kagutsuchi. Mu obtained the true Blue, so she did not need a Blue Grimoire to become Kusanagi, and it also allowed her to be smelted without the Kiln, just in the cocoon, though she still needed something to collect souls – this something was a monolith.

The 5th Hierarchical City of Ibukido had a monolith that was connected directly to the Kiln, but it was destroyed – this Kiln was sealed with the Kushinada’s Lynchpin.

The Kilns can also kill somebody by mostly reducing their body to almost nothing by sending them into the Boundary. In fact, only being near a Kiln itself exposes oneself to various side effects of the Boundary. Noel Vermillion and Bloodedge regained some of their memories by simply looking at the Kiln. Hakumen and Jūbei, while being near a Kiln were also weakened to the point that it enabled Yūki Terumi to overpower both of them at the same time.

The Kiln itself is like a living organism, as it has its own “life” and “pulse”. This can be detected by those that wield the power of the Blue, as well as those with the Power of Order. Destroying one is a simple task, but only by utilizing the power of the Blue it is possible to truly kill it. It is possible to restore a killed Kiln.

The Magic City of Ishana has an artificial Kiln in the sanctuary, but it cannot be opened. However, it still can extract the Boundary’s energy.

Trivia

 * The word Sheol is pronounced “Sheh-ol” in Hebrew שְׁאוֹל (She'ol), is the “grave”, “pit” or “abyss”, indicating that the Sheol gate translates into “Hell’s Gate” or “Abyss’ Gate”.