Chain of Fate

The is what binds souls to their living body. When the Inga no Kusari is broken, an erosion will take place from the end of it after being broken. Once this happens a gradual process of Hollow transformation takes place. A sign of being a step closer to becoming a Hollow is when the soul with a broken Inga no Kusari starts to feel hungry. The erosion of the last piece of the Inga no Kusari is far more painful than that of the previous ones (the Last Erosion.) Ichigo Kurosaki was able to fight the Hollow transformation but gained Hollow powers inadvertently anyway. A soul that is still linked with its body will feel that the chain is hurting them, as Orihime Inoue states when she dies from a shock because of a blow received from Acidwire.

For more information on the Inga no Kusari's erosion, see Encroachment.

Shinigami
The on a Shinigami is just as important as the Inga no Kusari is on an plus. While there is no chain per se connected to a Shinigami, the area where the Inga no Kusari was originally is still just as important as when the Shinigami was a simple soul.

In a Shinigami, the Saketsu acts as a boost to spiritual power, in conjunction with the, the source of spiritual power. These two points are commonly considered pressure points. If they are pierced, they seal up this spiritual power, and the Shinigami will lose all their power. The Shingami who experiences this will never be a Shinigami again.