Kushinada’s Lynchpin (クシナダの楔 Kushinada no Kusabi) is a weapon smelted by Shūichirō Ayatsuki before the Great Dark War. It interrupts the flow of magic element at its source, and if driven into the Boundary, it’s said to have the power to stop the flow of this element entirely., but once driven there would be impossible to locate or retrieve.
The lynchpin, in order to function, requires a living organism to become its core, a soul with the power of manipulating life energy. When its core’s life ends, the effects would end, too. 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, the lynchpin turns itself off, and the world is again filled with magic element.
Whereabouts of this weapon went missing at the beginning of 2107, the Void Information Administration Bureau and the Magic Association initiated separate investigations in order to retrieve it. The Administration Bureau was also observing Celica, as she was mentioned in Ayatsuki’s reports. The lynchpin was actually retrieved by Nine. It was hidden and sealed deep below her workshop, that was located in the basement of her house in Magic City of Ishana. Four months before the Black Beast’s reappearance, Nine unsealed it in order to borrow its power.
Before removal of the core, the lynchpin was described as being silver, with lines emanating green light, and now it’s red with orange light.
Tenjō Amanohokosaka’s soul being compatible with the lynchpin would indicate that she herself had at least minor powers regarding control over the flow of life. As the extent of her power is unknown, it can’t be specified how long it will remain active.