Ouga

Ouga is Ura's younger brother. Though he loved Ura as a child, he grew increasingly jealous and bitter over his brother, whom he felt their parents favored. Ouga turned to using darkness, a power forbidden for any demon to use, in order to kill his father and brother. He infected their father with the illness that is killing him, and later kidnapped Yayoi to use her as bait for Ura. source: wikipedia