Kouki

Kouki (光酒 Kōki), also known as the Sake of Light, 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.

It is used by Ginko in Episode 11 to attract Mugura when trying to locate Mujika on the mountain and then in an attempt to save him.