Kouki

Kouki are embryonic mushi that flow in the River of Light.The Kouki is the origin of mushi life, it is the basis for all mushi.

Description
The Light Vein flows through the Kouki. It is basically Life itself so to speak. If one can manipulate it then that person can use it for Immortality and Resuscitation.

In Episode 1 the Sake of Light that is drunk is made up of Kouki that turns half of the girl who becomes the grandmother into a mushi.

It is referenced again as the source of the Kouda's energy in Episode 7.