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 can not survive on the other side. When the original prime field device was sent to the heart of the Boundary, it gained a soul and also became the Eye of the Azure, becoming godlike.

The humans feared this, so they tried to eliminate it, but failed in doing so. They then decided to seal it away in the deepest part of the Boundary. The humans then proceeded to create copies of the original prime field device, known as Murakumo Units, to try and harness the power of the Azure. As soon as one returned from the Boundary, its emotions would be sealed, turning it into a weapon that could be controlled.

As of now, only fourteen have been created, and only three are known. 01 was destroyed by humanity using Sealed Weapon Izayoi and two more Murakumo Units were killed by Ragna the Bloodedge before the events of Calamity Trigger, meaning that out of the fourteen units, at least five of them have been eliminated (or in Mu-12's case, she became Noel Vermillion).