Black Suns are dark orb shaped substances that display some degree of consciousness. One was levitating over Yu during the dark ages of Greece. Many were seen in Yu's memories by Mikaela who could observe them.
They appear as a non-corporeal substance that are capable of being suspended within large containers, but can 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. The number of tentacles were up to seven of various lengths and these could also hang below the being when stationary. There was what resembled a single white oval eye within the mass. This was situated towards the top of the orb, different ones could have a varied amount of lights, of different sizes, within them, with one to three per being observed.
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.
When Yu reached into Mikaela's chest and awoke in a dream world of Nagoya with a coliseum encircling it, at least twenty one of these orbs appeared above the wall. Generally aligned horizontally they directed currents of lightning at Mikaela. They maintain their position around Mikaela and Yu in the coliseum but do not act further, not even as they continue to clash and Yu is flung into a building. Their lights are not visible during this time.
A memory of Yu escaping Sanguinem is seen by Mikaela, although the former as a child apparently cannot see what Mikaela can, namely at least twenty three black suns floating in the air above the city. They are also present, where none of them have any lights, in the memory of when Yu met Guren Ichinose with Sayuri Hanayori and Shigure Yukimi.
Powers and Abilities
Whether though being made to or acting of its own accord one substance could extend many tentacle like extensions and make contact with Yu's head. Each could generate a single long ranged jolt of what appeared like electricity, apparently from within their bodies, and direct it. Collectively they could cause an lightning explosion reaching high upwards into the air. This electrical power, along with some accompanying shadows appeared to have been drawn upon by Yu who could have it swirling around his sword.