Kushinada’s Lynchpin

The lynchpin is a device created by Shūichirō Ayatsuki during the First War of Ars Magus. It's 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 wasn't there stating, somehow it slipped from (his) grasp.

During Relius' arcade mode in Continuum Shift Extend, if Bang Shishigami is fought and beaten, Relius will comment: ''Truly... Staggering. But that thing you carry... Is that the lynchpin...!?''. Making it likely that Bang's nail inherited from his master Tenjō is the lynchpin.

It's 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.