Ryuusai Enoki

Old friend of Abe no Seimei and a powerful onmyouji. Fifty-five years ago, Ryuusai accompanied Seimei to Izumo to check a disturbance there despite objection by Seimei not to follow him. There, he and Seimei met Chigaeshi no Miko who he fell deeply in love with. He was soon manipulated by Chishiki no Guuji to kidnap the Priestess and break the seal of the Underworld and made to believe that by doing so, he could get the Priestess all for himself. Guren and Seimei tried to stop Ryuusai, but he uses the Baku-kon spell on Guren and made him try to kill Seimei. Guren finally killed him, but his body was used by Chishiki no Guuji's soul. (Source: Shonen Onmyouji Wiki)