The Nise-Kazura is a rope-like mushi that absorbs sunlight in order to survive. When sunlight is not available they burrow into the bodies of the dead so they can get more sunlight. They remain in a host until they are strong enough to migrate from that place on their own.Once strong enough the Nise-kazura turns black and becomes visible even to normal eyes.
In episode 13 all the stronger Nise-kazura join together to form a bridge like structure to migrate, this phenomena lead to the legend of the "One Night Bridge" in the village.
The Nise-Kazura don't break when pulled in the opposite direction but when one pulls them in the same direction they break easliy.
They have an affinity towards sunlight.