Kushinada’s Lynchpin

Kushinada's Lynchpin (クシナダの楔) is a device created by Shūichirō Ayatsuki during the First War of Ars Magus. Its purpose was to be "the nail that will nail (the entrance to the Boundary) shut". He also made mention of a key, referring to it as if it were something to be raised, and that the lynchpin was incomplete without it.

After seeing Relius Clover get devoured by the Black Beast, Shūichirō decided to use the lynchpin - however, the key was not there - stating, somehow it slipped from (his) grasp.

During Relius' arcade mode in Continuum Shift Extend, if Bang Shishigami is fought and defeated, Relius will comment "Truly… Staggering. But that thing you carry… Is that the lynchpin…!? "This implies that Bang's nail, Phoenix: Rettenjō, that was inherited from his master Tenjō, is the lynchpin.

It is meant to be powered by Celica A. Mercury (and would have killed her), and as of Phase 0, it was in Shūichirō's old laboratory. Later on, it was moved to the deepest part of Nine's workshop.

Interestingly enough, before removal of the core (which was turned into Rettenjo), the Lynchpin was described as being silver, with lines emanating green light.

As the Lynchpin requires a constant, controlled energy source - which would work where electricity and magic doesn't - the only viable option is a living Soul. What's more, a simple soul isn't enough; only a soul of someone adept at controlling the flow of life can be used as its key. The more adept a person is at it, the more effective and lasting its results would be.

After the soul is merged with the core, it is being constantly drained of its life. After the two bodies are merged, they will never come apart again. The person themselves remain conscious, alone, slowly watching as one's life is being eaten away. After the soul is consumed, Kushinada turns itself off, and the world is again filled with Seithr.

According the Kokonoe's calculations, Celica's soul would be able to fuel the Lynchpin for about 3–5 years.

Tenjō Amanohokosaka's soul being compatible with the Lynchpin would indicate that he himself had at least minor powers regarding control over the flow of life. As the extent of his power is unknown, it can't be specified how long it will remain active.