The Black Flame Attack is one of Byakuran's more powerful techniques, used after his wings turn black. Before Byakuran uses this technique, black roots shoot out from his legs and implant themselves in the ground to stabilize him. Next, Byakuran concentrates black Flames from his hand that rotate at an extremely high speed and then releases it as a blast. Although the flames are black, they are still sky flames, not flames of night.
The power of this technique is unknown, but it was able to hold a full powered X-Burner at bay for a while before it finally gave way.