Kiln

The Kiln (窯), formally known as the Sheol Gate (シェオルの門), sometimes called Yomi Slope (黄泉坂) or Judgment Gate (裁きの門) 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 World Void Information Controlling Organization facilities.

The Kilns are used to access the Boundary, some characters used them to travel in time or between possibilities, and Arch-Enemy Event Weapons and 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, Murakumo Units, are smelted in the Kilns. Similarly to an Arch-Enemy, it takes thousands of souls to create a Murakumo Unit, which explains why the Kagutsuchi Controlling Organization branch was completely empty. Hazama had sacrificed the Controlling Organization soldiers inside the branch so Mu -No. 12- and Nu -No. 13- could be smelted. Smelting the perfect Prime Field, Kusanagi, requires a Murakumo Unit and A Blue Grimoire, which is a portable Kiln whose purpose is to gather souls to smelt the sword in its body. The failed merge of Blue and 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 Arch-Enemy is actually a compressed Black Beast.

Nu was smelted in the Kiln at the bottom of the 13th Hierarchical City "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 a Kiln, just in a cocoon, though she still needed something to collect souls, this something was a Monolith.

The 5th Hierarchical City "Ibukido" had a Monolith that was connected directly to the Kiln, but it was destroyed, and now this Kiln is sealed with the Kushinada's Lynchpin.

Magic City Ishana has an artificial Kiln, which cannot be opened, but can still extract the Boundary's energy.

The Kiln can also kill somebody by mostly reducing their body to almost nothing by sending them into the Boundary. In fact, only being near the 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 the 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.