Ouga is Ura's younger brother. In his childhood, he loved Ura dearly, but as time passed, he became increasingly jealous and resentful of his brother, believing that their parents favored Ura. This resentment led Ouga to seek forbidden power—the darkness—which he intended to use to kill both his father and brother. He infected his father with a fatal illness and later kidnapped Yayoi to lure Ura into a trap.
However, the more Ouga used the dark power, the more it began to consume him. Yayoi and Ura managed to save him from being completely overtaken by the darkness, but while he was unconscious, an unnamed demon took him away.
Source: Wikipedia
