High school dxd: The God of Death

Hela, The Norse Goddess of death. A woman whose powers surpasses the heavenly dragons falls in love with a human man and has a child with him. They name the boy Issei and he was raised by his mother to master his powers. Issei's happy life was cut short when he found his father, and his mother dead. Issei went down a dark path and unleashed his range in the Great War. Bringing down the faction leaders and leaving their heads on the battle field. This is the God of Death's story.