Dark Ray was the first God of Death. He was present at the war 10 years before the main storyline of the series, and with Sword, laid the ending blow to Kurohime.
10 years later, he and his Angels of Death attacked Kurohime. He gave a fatal blow to Kurohimes alter ego, Shirohime, as well as fatal blows to his own Angels, stating that Angels and Humans were on par and equally disgusting. He was later killed by Kurohime and Zero.
Much later, in the land of the dead where he is reduced to a soul like any normal human would be, he is destroyed completely by Yashahime, who claimed to love him, for having become weak. Zero would then inherit his power and become the second god of death, Dark Rei.
Powers
As the God of Death, Dark Ray was a higher god, and had significant powers. He was able to summon souls of deceased humans and gods and use them as weapons, or interrogate them as he did with Moai. Using a the soul of a dead baby as a shield, he was able to defeat Kurohime. In addition, by summoning dead souls with exceptional regret or hunger, he created skeletal monsters who were able to eat human souls by touching humans, giving him more forces and armies.
Darkray wielding his six Death Angels — Sword, Axe, Lance, Mace, Hammer and Dagger — in their weapon forms.
Dark Ray had a small army of Angels to do his bidding, each able to turn into a weapon for him to use in combat. He was also able to use his strange body in unique ways, such as creating limbs and weapons from bones, and using his skeletal rib-cage as a weapon.
Finally, as he presided over the world of the dead, Dark Ray was able to open a gateway between the two worlds called the River Sanzu. When he entered the human world, a river of blood appeared, surrounding the area. Anyone within the star shaped perimeter was unable to escape as the river dissolved anything inside of it, and "entered" the land of the dead by dying.