Black Suns

The Dark Substance is an unofficial term used to refer to the dark matter that was levitating over Yu during the dark ages of Greece.

Appearance
It appeared as a non-corporeal substance that was capable of being suspended within large containers but also float freely in the air. The substance individually was around the size of a human head and whilst spherical in appearance it could extend what began as short tendrils into longer ones where they could make physical contact with someone. There was what resembled a single white oval eye within the mass.

Osaka Arc
This dark substance is remembered by Asuramaru when he was the human Ashera. Multiple forms of them were seen in large containers in a room where Sika Madu and Yu were present. One is levitating above a throne Yu is sat on and after Ashera demands to know what Sika Madu has done to him, the dark substance silently extends tendrils touching Yu's scalp.

Powers and Abilities
Whether though being made to or acting of it's own accord one substance could extend many tentacle like extensions and make contact with Yu's head.