Prime Field

Boundary Interface Prime Field Devices are artificially made human-like beings, with the zeroth believed to be created by Relius Clover, the first created by Relius Clover and Shūichirō Ayatsuki on a request by Yūki Terumi, and units 2-10 created by other companies and organizations.

They were originally designed to explore the other side of the Boundary, as humans cannot survive there. However, they constantly met with failures, again and again, until finally one of the test subjects somehow managed to reach the heart of the Boundary, the Azure. By coming in contact with it, the Prime Field has developed emotions, grew a soul and obtained the power of the Eye, becoming godlike. Fearing its power, humans tried to destroy it to no avail and in the end have sealed it deep within the Boundary. This, however, was not the end. Humans realized that if they could tap into the power of the Azure, then they could dominate the battlefields with it. This is why the next Prime Field Devices were outright weapons of mass destruction and not simple recon units. The moment that one would come out of the Cauldron, its emotions would have been sealed, turning it into a puppet. The special weapon-type Prime Field Devices were dubbed as Murakumo and Kusanagi, as they were meant to be weapons (swords) wielding a godlike power.

Shūichirō Ayatsuki attempted to create a separate system that would replace the Takamagahara System. Something that could enter the Boundary and even make contact with the Master Unit, the Kusanagi. Before Mitsuyoshi could stop the smelting process under Clavis' orders, the Black Beast had emerged.

The first Kusanagi was requested by Yūki Terumi and along with him, Relius Clover and Shūichirō Ayatsuki participated in its creation. It consisted of three notable elements, an Azure Grimoire, Zero-Type Prime Field Device and Murakumo Unit. Its final refining process was scheduled for 2099/12/31. However, the Black Beast has emerged from an even deeper part of the Boundary, terminating the experiment. Its current status remains unknown.

Multiple Murakumo Units were made afterwards, typically by different companies; one such company being Sector Seven with the creation of Mu -No.12-. It is hinted that Relius Clover oversaw the development of Lambda -No.11-. Relius, Kokonoe and Roy were present at the birth of Nu -No.13-; as such, she can be seen as a collaborative effort between Sector Seven and Relius.

Noel Vermillion was the first and only subject from the Murakumo-types to contain the true power of Azure. This allowed her to become the only known complete Kusanagi. It's soon revealed that Noel was the Original Prime Field and that she is also the Master Unit herself and used Mu as a vessel.

As of now, only fourteen Murakumo Units have been created, and only three are known. Number 1 was destroyed by humanity using Sealed Weapon Izayoi and Nu's body was destroyed two times by Ragna the Bloodedge before the events of Calamity Trigger.