Board Thread:Questions and Answers/@comment-200.246.78.2-20160920163144/@comment-8695373-20160921174050

The Lynchpin interrupts the flow of seithr at its source. So if it is activated in the Boundary, no seithr will come out of the Cauldrons. If it is activated in a world, all "free", flowing, seithr will disappear, but seithr that has a fixed form (a person, a chair, Ragna's right arm, Black Beast) will still exist. According to Kokonoe, if during the Dark War the Lynchpin was activated with Celica's soul, the Black Beast would stop its activity from 3 to 5 years. Not die instantly, just stop being active.